Stick with the 52x458s for the bullet selection, the Hornady 458 325gr FTX is a good cheaper pointy bullet and performs great upto at least 2300fps. You wont get them moving faster than about 1975fps most likely but they still work fine at that speed.

Ive got some Speer 458-350gr bullets coming. They should really make good use of the 1-26 twist but don't expand much at 1400fps or less.

Any of the Lehigh 458s should work really well without the extra weight. I haven't tried them yet in the 52. I have shot some Barnes 300gr 458 SOCOMs but just to see if they would blow the sabot because they are a boattail. Both are on my list for 52cal testing.

Ive only tried 2 .475s. The Speer 275gr which is really short in the sabot and the 325gr XTP which is about perfect.

52cals are a bit of a powder hog. You may want to start at 110gr with any sabot or bullet weight. BH209 should get any 300-350gr bullet well into the 1900fps range or more accurately. Knight and a few other reviews were getting roughly 1930fps with a 375gr RedHot but those are very expensive. They used a max load of BH209 or over 130gr of T7.

Mine was a semi custom LRH build and its still in the works so i haven't done any work on groups yet with the cheap little scope im using atm. It looks very promising though with a max load of BH209 and the 325gr FTX.