Answering your question directly, shooting a 3 under tillered bow with split fingers won't make much difference out to about 30 yards. Beyond that you may see a significant difference, but I can't tell you because I don't shoot further than that.
I've asked a couple of well known bowyers how much difference the tiller makes and whether you can switch back and forth between split and 3 under. The answer has always been that it really doesn't make that much difference at hunting ranges and you can solve for any difference you find by adjusting your nock point so you hit what you're looking at.
So, if it was me, I'd go shoot the thing and see where I was hitting. When I was getting consistent groups, I'd make whatever changes I needed, either of nock point or shelf/riser pad I need to get the bow to shoot where I was looking.
Take a look at Rick Welch's Accuracy Factory video; he has a good discussion of those adjustments.