Visit the home sites of each manufacturer and see if each one has run one of the typical tests such as Whetstone, DrhyStone, etc. If you can find the named tests, that might be at least close to an apples-to-apples comparison.
Note, however, that the amount of cache implemented on the motherboard makes a difference. I forget at the moment whether we are talking L1 or L2 cache, but you need to know that number to make a good comparison.