I highly doubt that little difference in pump is going to matter if "too big of pump" is your issue. I actually run the 625 pump with an A1000 regulator. I use the regulator as dual 6an input and the 6an out is hooked up to 8an return line. The pump is gravity fed slightly below my sump outlet (1/2" NPT) with a 100 micron prefilter and 10 micron on the pressure site. I've observed no issues with over-pressuring, cavitation, or hot fuel...nothing to indicate that an issue is anywhere close to presenting itself and I only make approx 500whp NA so the pump is theoretically 3x larger than I'd require.I adjusted my fuel injector flow rate and it pretty much fixed everything else. I had to bring the high slope down and then readjust the low slope, everything is working much better now. As for the fuel pump, it's not as oversized as I originally thought it was, but it's still bypassing a good amount of fuel. The pump is flowing about 150gph at 40psi, so it's still large, just not as oversize as originally thought. It's a Magnafuel Protuner 750, I plan to have it sized down to a 625 which flows about 110gph at 40psi, so a bit smaller, but it'll still support the power I'm making.