GPU-Z v0.4.8 supports the GTX580 and has fixed the memory clock monitoring bug on the Radeon HD 6870 and 6850.
Grab it if you want to use the latest and greatest - http://www.techpowerup.com/downloads/1898/mirrors.php
GPU-Z is a lightweight utility designed to give you all information about your video card and GPU.
Changes in GPU-Z 0.4.8
Added support for NVIDIA GeForce GTX 580 and future GF104 variants
Updated TMU/Texture rate calculation method. Please report any errors in the forums
Fixed memory clock monitoring on HD 6850, HD 6870
Fixed label corruption on cards without any shaders
Fixed rare CrossFire detection bug on ancient ATI drivers
Added voltage monitoring fallback for ATI cards with unsupported voltage controller
Updated PCI vendor ID for PowerColor
Removed MSI giveaway