David took my first thought when I read the title. Define "as good". Pure accuracy? Sure, just go talk to the bullseye guys. 1st shot COM from the draw? I think that is realistic. Multiple fast hits? No.
Look at it this way. We use a two hand grip because it let's us control the gun better than using only one hand. If you could get just as good a hits in the same amount of time with one hand, than your two hand shooting needs work. Some top shooters can get close if they are shooting big, close targets, but add distance or reduce the target size and the difference in performance will be there.
What percentage difference in performance is a reasonable expectation? I have no idea. Just try some drills two hand and SHO, see where you are at now and decide where you want to be.
If the group size is bigger SHO, then even though you are still down zero you have traded some accuracy for speed. In this scenario it was a good trade because the accuracy you gave up didn't cost you anything. But, if you gave up as much accuracy as possible and still be down zero when shooting two hand, then how fast would you have been? I would bet faster than SHO.The follow-up to that is whether you can get to be just as effective at 10 yards at a given speed with SHO as two handed grip? (In other words, could I still be down zero at the same speed, but maybe the groups are not as tight, so effectively, SHO and THG are the same?)
10 Yards, 4 shots, down zero, shooting as fast as you can? Two hand will be faster. For me it would be a lot faster, for some other guys, not as much faster either because they are awesome at SHO or they suck at two hand.