I had my 375 regulated with Kynoch 300gr (Woodleigh).

David Little at Kynoch says they produce an average of 30-32K psi. (that's half of SAAMI's 60K!) He even went as far as to test some from a specific lot number that I sent him and confirmed that they were in that range.

I posed the question at AR as to how he's doing this, and the consensus seems to be that there must be some special non-canister powder he's using.

That doesn't help you with a relaod, but it's the lowest pressure 375 ammo I've seen or heard of.

PS - the lowest pressure psi "Measured" load i've seen is from Accurate Powder.
300 gr w/ 83.0 gr of thier 3100 produces 2305 fps at 40K psi.
for 350 gr w/ 73.0 gr of their 3100 produces 2106 fps at 36K psi.