untill lvl 25-27 you are just usless(unless you are cav and can lance ppl)
WOOT ?
Even archers (on foot) start being dangerous at lv26.
And i believe a STR infantry is dangerous as soon as he has his weapon and 6 PS, even with 3 agi. So that's... dunno, lv15 ?
Thing is, as being said, the base melee skill has drastically increased. Just go in normal multiplayer once in a while, and... OH.
There's a lot of "peasant" guides out there, so take a look at them.
I'd reckon going full strength (who cares if you're slow), with 3 shield skill (to make sure you don't get shot before reaching the ennemy infantry), and a 2h sword. (with a thrust, else you'll get focused by cav too)
Also, join Siege, when you're fed up of duelling and want to level up, you learn way quicker than in battle.