Both my upper half's for my Bushmaster have 1-9" bbls. The 55gr and heavier bullets work wonderful with 55-64 being optimum for most .223 work.
I've never used RL-7 in the .223 but have used:
Imr and H4198, H322, Imr3031,Imr and H4895,Win748, H335,BL-C2,HodVarget, RL-15 and perhaps a couple of others. (In approximate burning speed order)
My advice is to try both your listed powders, but BL-C2, and Win748 will be the best with heavier bullets and longer barrels. RL-15 is also excellent.
My 14.5" AK upper-half prefers the 4198's at 22.0gr for both 55 and 60gr bullets. Most accurate load is 21.0 of H4198 and Hornady 60gr SP @ 2.225"oal shoots 0.75" with occasional better for 5 shots @100yds. 22.0gr gives a flat 3,000fps. All other powders are slower from abbreviated barrel.
The Flat Top Upper-half shoots better with a 55gr Nolser BT or Hornady 55gr V-max over either RL-15 (26.0gr @3,200fps w/20"bbl) and 27.0gr of Win748 or BL-C2 (3,250fps). Either will hold 1/2" 5-shots @ 100yds on calm day. All are loaded to 2.270" oal which is max for magazine feeding.
Try 22.0-23.5gr. of RL-7, and 25.0-26.5 of H335. I believe that H335 will give slightly better velocities. Accuracy should be slightly in favor of H335. I just haven't found it to be any better than the Bl-C2 or 748 in .223. In fact I found the BL-C2 to be best in .22-PPC as well for varminting accuracy and velocity.
However, in the .35 Remington, H335 is the "TRICK!" with the Speer 180 FN. 43.0gr of H335 gives 2,500fps and 2,500 ft/lbs with the 180FN crimped in groove in my Marlin 336. Ejection is effortless, but recoil is fierce, so's muzzle blast too!