Well, I don't think I've seen a 7.5 guy break 4 on the HTF. And a 6.5 guy should be way faster to first, so there are issues with both scenarios.
That said, to answer your question, I still think the 60 is a more consistent and accurate reflection of a player's speed. And while a really strong HTF can be a reflection of better field quickness (which is very valuable), it can also be affected by swing type and a few other variables. So, I would put more weight on the 60 and work on field quick. Both have merit. I lean more toward "you can't teach speed" which is more accurately reflected with the 60.