5870 or 7970 ?

[Mem5]

Hi,

I currently have a radeon 5870.

Single MD5 speed : 5018M

To get more power with oclhashcat, I would like to buy a 7970.

Single MD5 speed : 7670M

Is is a good choice ?
There are several models (950Mhz, 1000Mhz, OC edition, Boost edition,...) : which one to choose ?

Any hints about the noisiness ? (in dB)
About the cooling, better than my 5870 ?

Thank you.