Tec_41,
I do have 04 E-30's as surr./surr. back, (paired with E50's as L/R mains + an EC-35 at center) and tell you by own experience that I'm pretty happy with them. In other hand, you better hear what wafflebird said about the Infinity's though. Best bet would be to make an A/B comparison, IMO.
Cheers / Avliner.