I use my gps a lot as a speedometer. By sailing with it all the time for the last two years I know my approximate target speed for the wind velocity upwind and downwind. In short I use speed polars instead of angle polars as I feel I am more adept at reading wind speed than I am at reading wind angles.

Example: for a wind speed of around 12 knots I know I should aim for 8-9 knots upwind and 14-15 downwind. At 18 knots of wind I aim for 11-12 upwind and as much as I dare downwind (Usually 17-18 knots). If I'm slower than my target speed upwind I bear off, if I'm faster I know I'm not pointing enough. Same thing downwind in reverse, I get on one hull and then I aim for my target.

If I can't get to my target speed I know something is wrong somewhere.

Once I'm in the groove at approximately the right speed I fine tune in gusts trying to never dip below my target.

This technique is explained in excruciating details in a French ebook by Olivier Aguerre called " Elements de stratégie et tactique en cata de sport" (Google translate version) and I feel I made quite a lot of progress since I started using it.