My experience is pretty much spot on with rick's data, right down to the charge weights...
I've found I get about 100-150fps more with rl26 at about 1grain less powder than my h1000 loads in both my 6.5rsaums using 140 hybrids and 143 eld-x's...
Both h1000 and rl26 are giving single digit sd on my magnetospeed...
Here's my loads:
Gun #1
140 hybrid H1000 60.5 gr 3045fps, rl26 59gr 3140fps
143 eldx rl26 58.8 gr 3140fps
Gun#2
143 eldx rl26 57.7 gr 3070fps
Gun#2was very temperamental in load work up and didn't seem to like 140 hybrids no matter what I tried and took a lot of testing to get it to shoot the eldx's, had a very narrow charge load (maybe over .3-.4gr) where it would go from scattering them over 1.5 moa to under 1/2 then back to over 1.5....
Gun #1 will shoot almost everything I load in it well, except the load for gun #2, it shoots like crap....
As far as max pressure I think in gun #1 I hit 3200fps with h1000 Before pressure and I hit over 3200 with rl26 , never did find pressure with it and quit because I was well above my targeted speed at that point and quit.
I'd prob say start around 55-56 gr and work up...