450, my own thoughts on cast bullet meplats run towards the .390" as being quite good (perhaps a bit larger than necessary for cavitation to happen, which is the reason for them. I see a flat meplat as necessary to prevent detonation in the magazine as well as to produce a more grievous wound.

That is what is needed in my opinion for large game when using bullets that are hard enough to shoot at higher speeds accurately. I would certainly call 1,700fps to 2,000fps are higher speeds.

I have heard .460" hard cast bullets shoot better in micro-groove barrels. Seems to me the late Paul Mathews used larger cast bullets in his micro-groove as a general practice and found the undersized bullets that were paper patched would obturate at lower speeds to shoot well with smokeless, but only with exceptionally fast burning smokeless like 4198.IIRC

I just checked the meplat on the Bullet Barn cast 450gr. bullets I have loaded up for my Pedersoli 1886/71 lever gun and they run .300". I see that as being sufficient for deer, elk and moose. Your .390" meplats are considerably larger than that. My velocities are also in the 1,850fps range with a bevel-based, hard cast bullet. I do not expect poor penetration, but actually shooting something with them will show that.