Erick Silva has great technique, he's fearless, and he's very aggressive... as far as the GSP question goes, I'll simply say out of those three traits GSP only has one. That isn't to say of course there isn't a list of things GSP outshines him in.
Either way, as my sig does read, and has read for a very long time... Erick Silva is the future of the 170lbs division.
Also, to the OP... men tend to "peak" more in their very early 30s physically... so if he stays healthy and active, we haven't seen the best Erick Silva yet. Of course the same can be said or GSP.
Connor McGregor - Frank Edgar
Gil Milendez - Anthony Pettis
Carlos Condit - Erick Silva
Anderson Silva - Mike Bisping
Lyoto Machida - Jon Jones