RE: Does anyone know 243 load that is above max?
the .243 with good 100 grain bullets is totally and completely adequate for taking whitetail deer (and a lot more) as-is!
Use any reputable reloading manual and develope a load.....chances are you'll end up about 3000'/sec.....if you achieve 3,200'/sec your gain will be insignificant.....Even at 2,800'/sec it'll be totally adequate for deer.
If you really want a faster 6MM get a .240 Weatherby.....but it still won't kill deer deader or faster than a .243 Winchester loaded to reasonable pressures.