Ted-
Just to let you know that the .375 Winchester brass is on Winchester's "seasonal" list for production. The brass is currently available from many sources like Midway, Graff's, Weidener's and MidSouth, but may dry up again in the future for quite some time. It might be a good idea to stock up on some brass.
The post that Cub mentioned was posted in January, 2001 and is titled "375 Winchester." Mr. Stanton listed two loads with the BTB 250g LFNGC .377 dia bullet. They are both worth looking into as they outpace anything else I have seen listed for the 375 Win with a 250 grn bullet.
The best powders seem to be RL-7 and AA-1680 for this cartridge. A check of my manuals shows load data listed by Barnes, Hornady, Accuate Arms, Sierra, Speer, Lyman, and Hodgdon. In jacketed bullets Hawk has the best selection in F/P's listing a 180 grn, 200 grn, 250grn, and 270 grn; although I doubt you could beat the performance of the BTB 250 grn LFNGC at 2200 fps that Mr. Stanton has worked up in his rifles.
Good Luck,
-Dutch