I don't have the WSM. I do have years of experience with .277's though.
I have never shot the 90's because it's poor BC and you have to get into other than 10:1 twist barrels.
I've only used 100's and prefer the 110's. The muzzle velocity is only 80 fps apart and by 200 yards the 110 is going faster.
I achive the highest velocities and accuracy with IMR or H-4350. With about 60.6 for 100's and 60.0 with 110's CCI 200 and loaded to about .003 from the lands. Speed is @3590 for 100's and 3510 for 110's
The 270 wsm case holds about 6-7 grains more than my cases. So these would be good starting loads. I have found that the most accurate rounds are often @100 or so feet per second slower than max acceptable for reloading case life. In my guns the best groups are made with MV's of @3400. But I use 140 HPBT's for paper so it's a moot question.
I used to even use 100 HP's until I figured out that there is no difference in damage and it has a lower BC so why use it. The 110 @3500 fps is also very destructive to small animals.
IMR 4320 or 4064 use about 7-8 grains less powder at max pressure and also loose about 200 FPS. On the other end I tried IMR 4831 and R-22 with the cases clear full and compressed at 64 grains and the speed was also 80 or so less. My advice is test powders really close on the burn rate chart to the 4350's for 100-110's
In the 140-150 grain bullets the r-22 IMR 7828 and H1000 shine.