Chad,

On the GL-235, there is an option to have a 220v relay vs. a 110v relay (mine only has the 110v). I would opt for the 220v if you think you are ever going to get a 2 speed, 220v pump. That way, you should be able to use the GL-235 to DIRECTLY kick the pump up to high speed (or, possibly even to have it go to low speed from off, not sure how that would be wired though).

With the 110v relay option, you can only turn on a 110v booster pump (or use it as a non-powered switch like I am doing).