Jorge:
I do it all the time, but I prefer TMAX 100 over the 400. The 400 is not as good as TriX. The TM100 is a very good film, sort of in between Panatomic X and Plus X. FP4 is also a favorite of mine and I use it frequently. Currently I'm trying out some Fomapan 200, which I've never used and I still have no idea what my development times should be with D761:1. I prefer the 1:1 dilution as it doubles the mileage for a gallon of it. Plus I can't see any difference in negative quality between straight and 1:1.
Back to your question. If two films require the same development times in D76 there is no reason I can think of to develop them separately, thus using twice as much developer in the doing.
Ted