Hey Pepler - Don't take me too seriously, it's just that the idea of the "best" anything is pretty silly on face. I think I got a pretty good idea of where you are coming from from your original post, and I didn't mean to imply it was a dumb question or anything like that....it was just phrased in a way that lacked focus like many other queries I read here and consequently was left open to mono-component/myopic answers with no real useful explanation as to why the person thinks so or where they are coming from. You'd probably get those anyway, even if you were more specific. I'm a notorious chain-yanker from way back, pay no attention to the man behind the curtain, he is weak and feeble minded.
So mid -80's efficiency will likely limit you to more powerful SE amps such as those running with multiple tubes in parralell. I would not go for any 8 watt solutions as you may be sadly disappointed by that combination, even if the 2.5's are easy to drive you still won't be able to get much volume out of them without distortion. Moderate volumes may be just fine though, but I'd find that pretty limiting myself. The 20wpc of the 300SEi you mention may be adequate, but I know absolutely nothing else about that amp. Again, I think the realy beauty of SE amplifications comes in pairing it off with the right speakers so they can really shine. If you have heard enough SE amps with enough of the kinds of music you listen to to know that you want to go in that direction I would suggest also considering a more SE(T)-friendly pair of speakers....I think you'd be much happier that way. Just one opinion among many though. But then again, I AM the great and powerful Oz!
If you do like to listen to very complex, layered, dynamic music such as orchestral and rock I would also suggest you may want to try listening on an SE settup as I'd say, from my experience that would be the only area of potential significant weakness in comparison with other types of amplification. If that were my programing of choice, personally I would choose a different type of amplification for my system. Obviously it is not.
Marco