I was running mine 1.150ghz when comparing to a mates Galaxy S... Sadly the galaxy s owned my n900 in browser/general speed but just by a little.. and zooming/graphics yada yada are way more smoother as well.. only that i could play flash and galaxy s has 2.1 so no flash for em yet ;D.. anyways... n900 is growing old.. and still competes with the latest mobiles.. n i love it.. but this may all change once the nitdroid project is complete
To me anything that is designed to run at that speed will beat anything you have to 'jail break' to run at that speed.
The desire / nexus and other 1Ghz phones are designed for it, the N900 isn't designed for that, it might let you but it isn't the same thing.
I can only compare the HTC Desire and my under performing N900 @ 600Mhz, and in every way the 1GHZ is faster, but it is software related and buggy OS, not a CPU issue that slows the N900 down. Making it faster still leaves you with the OS.