I've had several AR's w/ 1-7" twist barrels... they seemed pretty omniverous to me.
I have a couple 'known-good' loads consisting of a 50-55gr bullet (doesn't really seem to matter which, but I usually stick w/ 52gr SMK because the boat tail makes loading easier) over either H335 or Win748. If a gun won't shoot sub-moa @ 100yds w/ one of those two loads... you've either got a problem w/ the gun, the scope, or the trigger puller
Both of the above loads shoot pretty darn well - may not win any BR matches, but not going to leave any points laying around in a reduced course HP Prone match either - from several 20" WOA 1-7" barrels, and one 26" WOA 1-7" tube. By 300yd the wind might start giving you fits, depending on the range, etc. but they should still group good.
For the heavier bullets from the 69gr SMK on up, Varget and RE-15 are probably the two most commonly used powders - because they work really well in a lot of guns. I've driven up to 90gr SMKs thru WOA 1-7" twist tubes w/ no stability problems out to 600yds, but 75-77gr mag length bullets and 75-80gr long range bullets are more common fare, and the 1-7" should handle them all easily. Other powders used include N140, N540, H4895, & TAC.
HTH,
Monte