Driver size aesthetics?

That depends entirely on the prototype.  Driver diameter was one of the engineering choices made when planning the eventual use of the engine, like gearing in a car on the road.  Low drivers will increase tractive effort; high drivers will increase speed.  Drag-freight era engines often had low drivers; when competition with trucking became a facet of RR business, taller drivers and higher speeds with shorter trains became more common.  Passenger engines often had higher drivers; in some cases, that was the only difference between otherwise identical engines of the same design, one version for freight, the other for varnish.  The track profile was another determining factor--the tall drivers which created speedsters on water-level routes were useless for mountain RRing.  Late steam designes using superheat and other modern techniques often compromised on driver size for dual-use engines.

Yes. NYC Hudson locomotives had 79" diameter drive wheels, while freight locomotives had 69" and smaller diameter drive wheels. Even the NYC Mohawks (4-8-2) had 69" drive wheels, except for the dual-service L4b locomotives which had either 70" or 72" diameter drivers (can't remember which). 

Typically yes (the IC built an experimental freight Hudson with a boiler from a Berkshire

and drivers of 73.5 inches diameter - the NYC J1 was 79", and some other roads' Hudsons

had over 80" drivers).

Simplistically stated: 

Hudsons and other large-drivered steamers sacrificed tractive effort for ease of running

at high(er) speed; smaller-drivered locos were more powerful "off the line", but were

not comfortably capable of high(er) speeds.

The driver size of a loco is effectively it's "gear ratio", and since these machines were the

very definition of direct drive (no transmission or gears) it was an involved process

to change that "ratio" by changing driver size, and this could not be done to an extremely

large degree at all - without a new frame, etc.

So, another advantage for the diesel-electric; they have far more in common mechanically with your automobile than they do with a steam locomotive.   

Pennsy K4s, K2s and most K3s had 80 inch drivers.    All the PRR Atlantics had 80 inch drivers.   There were passenger engines and built with more focus on speed.   By WW I PRR had standardized on 62 inch drivers for freight powers.   All H8,H9,H10 consoldiations (2-8-0) had 62 inch drivers.    The 2-8-2 L1s, 2-10-0 I1s and 2-10-2 N1 had 62 inch drivers.    The earlier H6 small consoldation had smaller drivers.  

The M1, M1A mountains built as dual service had 72 inch drivers but the frame and spacing was built to accomodate 80 inch.

the J1 2-10-4 super power built during WW II to C&O T1 design had 69 inch drivers.

On a steamer, driver size definitely affect top speed.   And as mentioned above smaller drivers meant better tractive effort.   An unofficial speed run for a Pennsy E2 4-4-2 was 127 MPH on the level track Fort Wayne div.    It had 80 inch drivers.  

so the J1 Hudson is a handsome engine and was built for passenger.   It would not have been very effective on a 100 car coal train.    ON the other hand a Pennsy 2-10-0 on the middle division would handle a 100 car coal train withjout much difficulty.

Driver size = gearing. Makes sense, got it.  I'm assuming certain freight items, i.e. perishables, were delivered by high speed, tightly scheduled runs which would be similar to passenger service

Hence the appearance of the "express reefer," which ran on passenger train trucks.

Yep, it's kinda like having a manual transmission with only one gear. The steamers were custom-designed for their local application, you could say.

You can just get a car rolling in say, third gear from a stop, and steam engines would do that by brute force, where your itty-bitty V8 gas engine could stall out.  

For example, you can get a good comparison looking at American Flyer S scale steamers. They all have the same size drivers, which is a good compromise for model production, but the sizes are also a good compromise between real-world freight and passenger diameters. The exception is the 0-8-0 with the small diameter drivers, which is a permanent "low gear" which is what the real locomotive would need to heave cars around in the yard.

The drivers on the Santa Fe 3460 Class Hudsons was 84". Long legs on those engines.

Driver size is like gearing, but its important to realize that steam locos had maximum torque at their lowest RPM and so that helped them "get going" even with big, big drivers.  

As to the aesthetics, I think both ends of the scale have their own appeal and can look good.  Large drivers look really good on Hudsons, Northerns, and Texas locos, etc.  - I don't like the look of any large-driver loco with two wheels that much, though (America, Atlantic).  A loco with smaller drivers looks good to me only when it has a lot of wheels: even six doesn't look that good.  The best looking small-driver loco I have is the BR-44, with five drivers a side.  Six would be even better.

As to the LC+ Hudson, it is not a scale loco but it has drivers that scale out to be "sorta big" and I've bashed it a couple of times into scale-size locos that look quite handsome.  The Adriatic below is scale size but built on an LC+ Hudson chassis, and as you can see the size and spacing of the drivers looks really good on it.  In the second photo you see it with the Lionel scale Atlantic which has much bigger drivers, but as Ii said, just doesn't look as handsome.  I think the spacing and number of drivers has as much to do with aesthetics as the size.

And then there were the 8-footers............

And some more Victorian aesthetics for you. The Crampton design had a large diameter driver towards the rear. No real pull but would go like h*ll with light passenger express trains.

The outside Stephenson valve gear makes them a pleasure to watch.

Great videos...

check out the "Garratt in HO scale with sound" video after the first Crampton video.....Tell me this loco in O scale would not sell like hot cakes...It is a beauty!!!

I find that locos like Lionel's 746 Northern with the streamed line cladding look top heavy with their smaller looking drivers.