Is it true that, around 1990-91, CSX was intending to restore an Allegheny? We all know they didn't, but... If I recall, the Allegheny had the highest axle load of any locomotive ever.
I've never heard that rumor, but in the early '90s, their management had such a good relationship with the 765 crew that they could pretty much take their engine anywhere they wanted and almost whenever they wanted. They certainly were very pro-steam back then...hence the 2765 season as a thank you CSX.
If I was to make a statement about the rumors I've heard (or not in that case)...I would say that CSX had no interest in starting a steam program and that the only (C&O) engine worse than an Allegheny would have been a 2-6-6-2. That being said, there were some attempts to get the 2-6-6-2 at Baltimore restored for a tourist line in WV, but that, of course, never happened. If I recall correctly, both surviving 2-6-6-6s would need the works...the running gear and everything. The HF museum was supposed to receive a later 2-6-6-6, but their engine ended up going back into service (briefly) so the 1601 was given instead. They are very few railroads in the country which could tolerate a 2-6-6-6s axle loadings. Probably the best locomotive for CSX would be the 490. That streamlined hudson is modern, powerful (50,000lb of tractive effort), and distinctive. While the Kananahs would be good too, I suspect something unique would fly better (there are already 2 berks of that design running...3 once 763 is rolling again).
You are absolutely correct at them being the heaviest axle loadings. They were so heavy that Lima fudged the scale house measurements in order to avoid weight penalties...it wasn't until the Virginian's lighter 2-6-6-6s were order, but had a higher official weight, that the C&O figured it out. That was actually a huge safety risk because of bridges. Lima actually lost money on the 2-6-6-6 design...not just from construction, but also the settlement with the C&O after the fact. Sadly, the C&O used them mostly in coal service and it wasn't until the end that they saw some high speed freight service...which is where they really shined.
The 2-6-6-6 design was actually a C&O T-1 (2-10-4) that was increased in size by 20%. The NKP berks were a 20% smaller version of the T-1s. So arguably, the T-1 was one of the finest designs of all time...the Pensy & C&O had T-1s, the C&O and virginian had 2-6-6-6s, and the RF&P, C&O, PM, and NKP had NKP berks. The T-1 was designed in the spirit of those fine Erie Berks...with the 70" drivers.