[msmith10]

Not a simple question and as far as I know there's no simple answer or formula. Folding prop will be faster, that's about all you can say. 2-blade, 3-blade? Wind speed?
At hull speed it won't make any difference. In light air it will. If you spend most of your time racing, you'll want the folder, but then again if you race a lot you probably have one already. If you race occasionally but have to motor 3 miles up a river against 4 knot current to get back home, you may just decide to eat the speed loss. If you'd prefer to motor than sail when the weather gets rough, go with the fixed blade.
If I recall, PHRF gives you 8 seconds per mile for a 2 blade folder over fixed, 12 seconds for a 3 blade. It will cost you more than that, otherwise every racer would have a fixed prop.
If I had the money for a saildrive, though, I'd definitely spring for a feathering prop (slightly more drag than folding but better performance).