I guess that I should put some numbers to my vague ramblings, and emphasise that what I call 'subtle' and what you call 'bigger grain' may indeed be two different things, as our words suggest.
Because my observations on increased graininess are based on my poorly controlled developing sessions rather than my well controlled sessions, I couldn't put hard numbers on anything. Even if I could, they might not be relevant to other process combinations. However, I try to keep post-development temperatures within 2 or 3 C (say up to 6 F) so your use of 60°F wash water after 68°F wouldn't seem way off - but it might be, and might the water have been even cooler? It seems worth checking as a source of the problem.
Counter argument:
Richard Henry, in what has to be one of the most lively technical books ever written*, Controls in Black-and-White Photography, says that this temperature control stuff is all a myth harking back to days when emulsions were softer, and backs up his opinion with the results of some tests with Tri-X in D-76. One of his tests included a change from 68°F dev to 62°F stop. He found no detectable change in measured granularity 'within experimental error'. He did, however, only test with Tri-X. Maybe that matters, maybe it doesn't.
So, it's a possible 'maybe' as far as I'm concerned. One of those cases where avoiding a potential problem is probably easier than defining it.
Best,
Helen
*and either 'Heretical And Only Fit For Burning' or 'The Honest, Iconoclastic Truth About Everything' (or something inbetween that's worth reading).