I just installed Debian Sarge with the netinst. disk using only the 'expert' option, not the 'expert26' option. The installation went smoothly, and I chose to install the 2.6.8 kernel halfway through at the designated prompt, to see what happened.
So far I've rebooted twice, and the speed seems fine. 2.6 is running, and no problems yet.
This is a bizzare problem however - it affected all distros I tried that booted to install with 2.6 by default.
I tried Suse 9.3, Fedora core 3, Mandrake 10.1, and Debian Sarge. All had some form of extremely slow performance.
As an example, on the Debian installer, booting with 2.6 - it took about 5 seconds just to draw the first selection box on the screen, the language selection one. It only got worse from there.
I have Etch running on my main workstation... 2.6.11, no problems.
I checked out that link syg - it sounds like this person is having some permutation of the same issue I am.
I'm going to keep trying to reproduce this problem...