Going "loud" with 5w on 92 db speakers may be possible, but at the louder levels, the sound and soundstage may begin to flatten out, not being optimal or providing the best sound possible with what you have. I'd guess the 45s would not cut it with your speakers, I think you'd be severly under powered. I think the 300Bs would get you to where you need to be. Or, consider making a switch in speakers, as the 45s are supposed to be well worth the switch, though the speaker options for less than two watts are relatively minimal and can be quite pricey.
Good luck.
