I say if your looking for really good accuracy with IMR4350, then you might think about trying the Lyman accuracy loads. With 174gr rounds they list 52.5, but be advised this is a max listing. Also this is not matched with the 174 Sierra MK, but a Hornady roundnose bullet. I have not tried this particular load.
I have though used the listing for 180gr Sierra ProHunter with 47.5gr. of IMR4350. It works very well. Best group to date was 1.75inches, 10 shots @ 100 yards. It is on the lower end of the velocity spectrum for x54r, but it is quite accurate. I used this combo in a match and it did very well.
Back to the SierraMK 174gr. - 50gr of AA4350 and an OAL of 3.00" works very well.
This is all for .311 or .312 (Hornady) dia. bullets, which is all I shoot.
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Went back and looked thorugh my notes. I have in fact tested a x54r loading with 52.5gr of IMR4350, with a 174gr Hornady FMJ/BT. Similar, but the not the same as the SierraMK HPBT. Five shots at 100 yards hit just a hair over 1.75 inches. This is the only test of that combo I have done, and just the one time, but it looks promising.