[EricH]

Originally Posted by Mr. Rogers

Would thicker center wheels help at all, or should I consider 8wd with the center 2 pairs as close together as possible (I don't want too much wear on the wheels this year)

You could also swap one end's omnis for a pair of traction wheels of some form. That'll give you--for turning purposes--a half-length, full width 4WD, instead of your current 2WD (again, for turning purposes).