Lee
Try the Speer 50-325gr HP too and the 50-300gr FTX. Both shoot great in my 54-120 with the red or purple 54x50 sabots. The reds only come with some of the Barnes bullets but they are tougher than the purples. Ive shot a bunch of the Speer 300gr for 50A&E too. They should be awesome for closer shots and a great cheap 50cal is the Rainier 50-335gr HP. Midway sells them for under $30/100 and they are made for Alexander Arms Beowulf ammo.
The Ultimate 50cal though is the Remington 385gr CLHP. Awesome bullet for $62/100 but they need a heavy charge to expand reliably. Recoil is a bit brisk too.
54x50s rock.