I like high speed on centers for the same reason as jdbolick. I have 90 on mine and he does a good job of picking up blitzers on the outside, while still being able to do a decent job when run blocking.
The same can be said about guards in the current sim... although my 90 speed guards did stupid shit a couple of seasons ago. I would say that guards are more support (pass)blockers in this sim, which means that for both Cs and Gs you can easily get by with 80 and FS. That'd be my goal if I were to make new ones.
On OTs it's much more important to have solid primaries than to worry about speed. which makes speed less important... if you can maintain a solid build and still get 80 speed, that's fine... most can't, though.
I think the target is probably 68+ depending on the final build (and no FS).