High powered single end 300b recommendations

one other consideration for you if you go to a Parallel or Push Pull 300b you will be replacing 4-8 300b's tubes when they go, worth it? they run what around $250 each these days for average ones. re-tubing gets costly fast. 

I’ll say it as no else will 86db speakers and 300b’s are not going to work.  I tried a set 300b amp (8wpc) with 94db speakers and it wasn’t enough. Parallel amp only 16wpc not enough. 300b’s do not sound great when driven much above 50% power so trying to get any volume and dynamics is just not going to be satisfying.  86db is just not efficient enough for a SET.  Maybe an 805 but I’d say that even won’t be enough (around 22wpc).  

your in push pull territory with 86db efficient speakers which is not hi. If you had speakers that were above 98db that would be another situation all together. 
 

sorry but that’s the reality.