Opinions? I know the general agreement is 1000 plus watts, but I've heard success with 300 watt Ampeg SVTs.
I would imagine the yba300 and some Acme's would rock. I use 400 watts per with my Low B2's. Usually don't have to turn the amp up much... maybe 10 O'clock on the master. eden WT800
1000W with a Low B4 sounds about right. I used to run a Low B2 with about half that much. Whether at Low B4 will work well with a 300W tube head depends on how loud you need to play and the sound you want. The sensitivity for the Low B4 is listed as 96dB 1W/1M. IMHO, the Low Bs are not super tight even with a big solid state amp. I suspect you might get a woolly mess in the low end with an all tube tube head due to reduced damping.