I don't think a 52x458 sabot is going to support a 458 that long but i would start low and/or just shoot a big 52cal Parker conical. Ive shot some heavy loads in the 54 with a big conical and its not fun or accurate. In a 52x458 with heavy loads, i would be looking at 325-350gr Speers or FTX 458s or maybe a 405gr tops. 130gr of BH209 and a 325gr is in the 3000fpe (1950+fps) range and still has a ton of energy at 100 yards.

I bet the Barnes 300gr 458 SOCOM would be plain nasty with a hot 52cal load without as much whiplash.