Do you think the highest payout would be keeping XTZ for more gains or rolling it over to BTC now? Still trying to make enough to get into the the island project.

Think of this way: XTZ will have a much easier time doubling than BTC will, which means it will be easier for your money to double in XTZ than BTC.

That said, BTC is the shit and so... it is really up to you and what floats your boat.