My experience:
I mounted a p90 in the the neck of my tele. First with stock 250k pots, later added brighter caps, then changed to 300k and stayed for a while... until I played a squier custom II to find that in comparison my antiquity p90 sounded muffled, lacking much high end

I have just changed the tone for a 500k but still it sounds muffled in comparison to the squier... so i guess I'll have to go for both 500k pots... or maybe even a 1Meg tone as someone suggested above?