Even though the OP suggested that a charged hit from a heavy twohander would crush a block, I still think this would slightly underpower twohanders. Even with this combat speed it's not too hard to block/parry a weapon with, say, 90 speed. If someone would use fast attacks with such a weapon vs me, I'd block and counter. If he charges his attack, I'd just do some swift cut to interrupt him. The problem would be that he
has to charge his attacks, otherwise his axe wouldn't even be much more powerful that my sword.
Anyway, this might work well if the bar would fill very quickly. For a 1h sword or axe, it would at max take a second to fill the bar. For a 2h axe, at max 2 seconds, but 1.5 would be better imo.
For feinting: I agree that a feint shouldn't completely empty the bar, but consecutive feints should. Feint one would drain a rather small amount, say 20% (perhaps this looks like much, but the bar would start refilling 0.2 seconds afterward), feint two substantially more (33%) and feint three a lot more (50%). The percentages I gave as example aren't fixed values, just to give you an idea. They would also depend on the weight/damage/speed stat of a weapon.
Not sure whether this is a good idea, but certainly worth a try. If there is going to be a .66x, I'd prefer to first see the current bugs (for me mainly instastab and parry unreliability) to be fixed (though indeed, instastab would actually be fixed by this system

).
It would perhaps work better if combined with Ares' running and gunning suggestion here: http://forums.taleworlds.com/index.php?topic=89026.new#new
I made a post in it that might also complement this system quite well: http://forums.taleworlds.com/index.php/topic,89026.msg2298973.html#msg2298973