Plated bullets are generally good on data thru 1200'ps with jacketed data. I looked at the Rainier manual and they show a max load at 6.3 grs 231powder, 230 gr RN COL@1.275. Speed was still below 900'ps. They show a max pressure at 19,900PSI with 21,000 considered a max average which is also the SAAMI pressure limit. I checked in the current Speer for jacketed data and it comes back a lot more than your load using 231. The call is yours to make.
Where did you find the 5.1 max data?