I am new to sarging, but I have more experience with internet dating and women (on a friend level).
First, what most of those sights won't tell you is a good minority of women don't pay. When they don't pay, they can't read your email or see that you are interested. I had the same exact profile and Yahoo was bad... Match was considerably better.
Second, the quality of the women is kind of like the street. 5% hot, 30% average and 65% (yikes!). Now a hot girl on that site, gets swamped with emails - so you better have a good subject header otherwise yours isn't getting opened.
To convert this into the PUA. It's like you walk into a bar where it is mainly a sausage fest and there is one hot girl. You open her, either your lucky, she stands there for a week until she responds or worse she never paid the cover and your talking to a cardboard cut out.

I'll stop here.
If you want to supplement your live activities with online activities - go ahead. But don't expect much. Make sure your subject lines are strong (as in relevant ) and keep your emails short.
Teddy K.