I appreciate the info. I've scanned the film and despite how the negs looked, they are useable. Funny too - this roll has a pink cast to it, while one I developed last week with the same time and temps looks normal.
My next roll will be developed 11.5 minutes. I will let you know how it comes out.
Funnily enough, I dev'd a roll of TMY400 (old formulation) pushed to 1600 just yesterday - before I'd read this thread of course! They look rather underexposed, but I can't actually remember when the roll dates from or what I was trying to achieve - I just found it in my 'pile of stuff I've shot but obviously didn't care enough to do anything with' with "PUSH TO 1600" scrawled on the side, so no judgements can really be made...
Anyway, I have a folder of datasheets for the films I use - the one I have for TMX/TMY is "F-4016: Kodak Professional T-Max Films" (February 2004,) and the times in that appear to be in agreement with yours: Viz. 6.5 mins in XTOL normal, 7.25 mins one stop push, 8.5 mins two stop push.
Personally I used HC110 dil B, but the times are very similar (6 mins rated, 6 mins one stop push (!), 8.5 mins two stop push.)
All the recommendations in the datasheet follow a similar pattern - e.g. for a VERSAMAT Model 11 roller-transport processor the recommended machine speeds are 5.5 ft/minute at ISO400, 5.5 ft/minute push one stop, 4.5 ft/minute push two stops.
I'm thinking the baseline recommendations in those TMX/TMY datasheets take a rather optimistic view of the film's latitude with normal development

.
Oh, and to get rid of that pink cast - fix, fix and fix again. I fix TMX/TMY for a good 50% more than "necessary" to lose the pink stain, although I've no evidence that it does any harm if you don't.