Considering 2-Rail, 8'x12' space

Totally subjective.  Maybe tossing up what your track plan might be vs. the room dimensions would get you more feedback as to feasibility and other considerations.

I have comparable space, but run nothing larger than 2-8-0 steam and trolleys which lets me have fairly tight curves, etc.

    I'm relatively new to 2 rail myself but thought I'd respond since my layout

   is so close in size to yours. Mine is in a spare bedroom that is 9x12. One 

   thing that caught my attention in your post is that you'd like to run modern

   UP and BNSF equipment. My hand built track has roughly 28" curves which

   I've found will let me run short 4 axle engines, a Red Caboose GP9 and an

   old Atlas Roco F9 set. 50 foot cars are the maximum. You might be able to

   go slightly wider with your curves as I have a bedroom door and closet door

   to contend with, but I think 6 axle engines and 60 foot cars would still be 

   tough to do. You might want to let the exitement of your visit to the railroad

   club wear off a little before you jump into something. As others mentioned

   it can be rough finding the same thing in 2 rail that you've seen dozens of

   in 3 rail. Personally I'm loving 2 rail O after being in HO for years. Just keep

   in mind you might have to make some sacrifices especially on the bigger

   modern equipment.

         Best of luck,

             Geoff

Thanks Geoff! I planned on using 40.5"-45" track curve radius from Atlas. I want to expand from one end out later on when I get a bigger space in the future, so track plan will be designed around this idea. Kind of like a 2 track oval for now and than expanded backwards out later! This area will be like a peninsula.

If you're using 40.5" radius Atlas, their 6-axle diesels are rated for that minimum radius. My personal experience with the MTH scale-wheeled 6-axle diesels (C40-8, C44-9, SD70ACe, ES44) has been they'll negotiate 36" radius with cars under 50-feet coupled to them. They're officially rated at 42" radius in the catalogs. The key is the track work has to be kink-free and properly leveled.

That said, I'd keep the equipment smaller for better operation and appearance.

I've been going back and forth for some time about building a small layout in a 12x12 spare bedroom with a corner entry door, so I can relate to your situation.

I'm building a 4 ft. x 18 ft. layout that is simply point-to-point. It's great fun just to be laying track, doing power and all the things you would do for a bigger pike.