Regarding the 215 v 315 difference: Yes, they are going to be different, I sure would hope so for the price difference. If you're looking at picking some up and you don't already have 215's, yes, the extra $40 is definitely worth it. However, if you already have some 215's, I don't think the marginal gain you will get from switching to the 315's is worth an additional $150 from where you are currently at. Unless of course you enjoy throwing all your money at your audiophilic addiction ;)
edit: also, concerning the high's - some people think the 215s are a bit shrill, while some think the 315s are a bit dull on the upper end. YMMV
edit: also, concerning the high's - some people think the 215s are a bit shrill, while some think the 315s are a bit dull on the upper end. YMMV