Max swing rate is one swing per 1.25 seconds, regardless of the swing speed of the weapon. If you have a dagger with 30 SSI, having 150 dex won't make you swing any faster than having 75 dex (although it would be nice).
My nox fencer mage uses a spell channeling no penalty dagger, I don't think it even has SSI on it and her dex is only 45, and she hits near max (or at max if I drink an agility potion, boosting me to 65 dex temporarily).
so with a fast weapon it's not too hard to do.
I don't know where to go to actually input numbers and have it tell you what exactly your swing speed is, but keep in mind if you are a warrior type predominantly (you have fencing, you have chiv, you heal with bandages instead of magery), then having a bit of extra dex won't hurt.
With a 225 cap I'd recommend:
100 Str
75 Dex
50 Int
IF AND ONLY IF you find a fast weapon to deal your poison with, like a dagger or a kryss. If it's a slower weapon, you'll need more dex.
If you eat a stat scroll and have more points to work with, throw them all in int. It won't hurt you a bit.