Out of a rest, not much, if any. The SP01 allows you to get a slightly higher grip. Combined with the added weight, it allows you to squeeze as much accuracy out of the platform as you can (ala SP01 shadow target, etc.), especially for quick follow up shots. If you are looking for the highest possible grip, SP01 or SA is the way to go.
For a field or range gun, both can be tuned to have excellent accuracy.