What is the top speed of 765? I have read rich mention on new river trips the got to 70 mph. Could it go 80 if needed for a 15 car passenger train?
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I've seen both 70 AND 80 listed as the top speed, so I'm curious too. One thing I have learned is to NEVER underestimate the capability of an NKP Berk. If the info about being able to move huge coals drags that is mentioned in Rehor's Nickel Plate Story is true, I will never doubt their ability to move ANYTHING.
With 69 inch drivers 70 to 80 would be tops, since they weren't counterbalanced as well as the N&W class J's they would never see 90-100 mph. They were built to pull freight from Chicago to Buffalo at 60mph all day long, and they did this well.
I have run the 765 at 79 mph on the B&O between Willard and Akron.
A good way to calculate how fast a given steam locomotive might be able to run is 110% of the driver diameter. 69" x 110% = 76 mph.
Some extremely well balanced locomotives (the N&W "J" for example) could go much faster than that calculation.
Here's some interesting numbers for those interested. These should be pretty close if my math is right.. 
69 inch drivers will produce the following driver rotational speeds..
MPH.... RPM....
60 293
80 389
100 486
110 538
120 586
Once you approach 400 rpm with the mass of rotational and reciprocating parts of a steam engine, it better be balanced well, and in very good shape. 
This is why the western roads, and a lot of passenger engines, had larger drivers to produce higher speeds with the same RPM.
I seem to remember reading somewhere that the N&W J at 110 mph was turning the drivers at 540 RPM. Most steam locomotives would tear themselves apart well before reaching that speed.
