Lyen seems like the only choice for a programmable controller, but the prices are relatively high and the quoted standard power ratings are disappointing. Locating a larger controller on the bike would also be a pain as there is no triangle.
Plus, the GM controller is really good for what it is.
I'll move to a larger controller someday, but not just yet
If the controller can take it and your wires are capable you can run up to 6kw. As it heats up, and it will fast then you start to waste power into more and more heat. Install a temp probe keep it cool and it will last.
BUT
To tell you the truth i'm getting tired of having to back off and let the motor cool down. Can only push it for short periods @ wot Searching for heavier motor at the moment.