Renewal: The need for dex?

I've read through the forum for a while and think this is the most suitable place to ask my question.

I'm a lv 87 Knight in iRo Chaos renewal server. My dex is 45+8 and hit 316. There are quite a few monsters I keep missing. (Like Noxious.) And this is without the blind status if anyone asks.
So to stop missing, do I need more dex? And how much dex is needed to make sure that I never miss any monster?
I'm an SVD knight by the way.