That's a tough one since most folks are pretty secretive about what they get paid. I can ask around but my only verifiable source was from an ex-Tier 2 Kelly employee that called in as a regular customer. She said she was getting $10 per hour and had no reason to lie.
I do know that if you are crossed-trained (e.g. iOS and CPU) you'll make more but if I had to guess I'd say T1 to T2 would vary between a $0 and $2.00 per hour bump.
Also, if you are currently part time and get chosen for T2 then chances are you'll go full time but beyond that I don't know of any bennies for sure. Most of the people I've run into at T2 don't know much more than anyone else (in some cases they're pretty clueless) but they had good stats and got bumped up.