5870 or 7970 ?

I currently have a radeon 5870.

http://golubev.com/gpuest.htm Wrote:Single MD5 speed : 5018M

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

http://golubev.com/gpuest.htm Wrote: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.
Yeah, a 7970 will be faster than a 5870, it's a better choice.
A 7970 is hotter than a 5870 though, by around 20-70W.
The higher the core frequency the better, if it stays stable.
Noise is usually written on the product page, but I can assure you the lousy stock turbine CAN be annoying.
Aim for two or more fans variant (assuming you have fans inside your case to blow the hot air out).
Oh, and don't forget the warranty(2y min).