You can go pretty low with Varget if you use correct wadding. I'm loading Varget in my .450/.400 3.25" NfB loads with a 265 grain cast bullet. It's great. Mention of it here:

http://forums.nitroexpress.com/showflat.php?Cat=0&Number=185256&an=0&page=0#Post185256

I think H4895 is a contender also.

Good luck and report back.

Curl