Surviving a rock concert: how much NRR?

We went to a Springsteen concert to benefit Kerry about 2 years ago. We definitely lost hearing. We're going again tonight, and the questions is whether to wear NRR 22 or NRR 30 plugs. This etymotic site has safe periods for use of their musician professional ear plugs (safe length is for NRR 20):

Etymotic fitting guide (PDF)

112 db Blues bar/Rock concert 5 MINS. 1.25 HRS.
Above 125 dB you are at risk for any period without maximum protection

Hmm. I think for a multi-hour Springsteen concert I'll put NRR 20 in one ear and NRR 30 in the other ...

Update 6/11: Well, it turned out to be a Zydeco New Orleans Folk Rock concert and we weren't all that close to any speakers. Hardly a real test - nothing like the Rock the Vote concerts. The NRR 20 material is a waxy glob that fills the external ear. Unbelievably geeky, but of course that didn't bother me. Unfortunately it made the music rather leaden. I opened a space on the right ear and that seemed to suffice without causing too much damage (I think).

As a concert it felt muddled. This type music really doesn't scale to a major venue -- it's way too intimate. On the other hand, it would have been great on Prairie Home Companion.

Sprinsteen must be getting bored of rock and roll, but it's really his natural home.