I stay at about 55% raw test max for speed days. Speed is the most important on these days... if you can move 45% a bit faster than 55%, then by all means go with 45%. Find a weight that works for you, and then stick with it through a training period. So for example, I am using 115 lbs free weight, plus 65 lbs band tension, for a total of 180 lbs, and I will stick with that weight for speed day until my next max. On days when I'm not using bands, I'll just use 185 straight weight.
Whenver you do a test max, or competition max, you can re-adjust the percentages for your new max, but like I said, speed is most important, so if you get a 10 lb PR on bench, technically your speed day would go up 5 lbs by percentages -- but you could do just as well to leave your speed weight the same and just move it faster. Hope that helps.