I think my success with the rear-only diff lock for auto-x is due to my
driving style and past vehicle experience and is not related to the tires. I
switched from yoks to a used set of BFGs for the 94/95 season, due to one of
the yoks getting trashed when my ex-spares car was moved. (Hi Chris! Jab Jab
:) I had the same success with the rear-only diff locked setup with the BFGs
and with the yoks.
I come from a big-block V8 waaaayyyyyy overpowered-type race vehicle (RA IV
455HO CP '73 Firebird) and enjoy a tail-out steer-with-the-throttle driving
style. The rear-only diff lock setup gives the 4KQ more of a
rear-wheel-drive handling style and all but dials-out the dreaded understeer
(along with appropriate tire pressure differential F&R & properly tuned
Konis). If you are coming from a FWD or heavy understeering or
underpowered-type vehicle (honda, etc) and/or use more of a finesse driving
style then the the all-open setup may very well work best. I like a
toss-it-into-the-corner and steer-with-the-throttle driving style, more
Pro-Rally like and certainly not a finesse style, but, hey, it works for me.
I did find that the hot setup with the ur-Q was with both diffs locked, but
we're talking almost double the HP of the 4KQ in this case.
Try experimenting, but then stick with what works for *you*.