Only one to buy in my mind for higher powered 300B, the Don Sachs/Lynn Olson Blackbird Monoblocks; manufactured by Spatial Audio Labs. Not cheap at $10,000 each, but it appears the culmination is Don's and Lynn's life's work. I do not own them, as they are not in my current budget, but I am lucky enough to get to hear them now and again in my friend's system. I believe they are 24 WPC?
He pairs them with the brilliant Aric Audio Motherlode XL preamp, which I also own