Prior to the encryption, I was benchmarking around 2800-3000 on Quadrant on the .211 leak, rooted, using SetCPU to force it into performance governor 1200max/1200min.
After full system encryption, including internal and SD storage, I'm averaging around 2400-2600. This benchmark also taken on Performance governor, 1200/1200. I've tried the Kernel performance tweaks in the development thread, but honestly can't say that I've noticed any palpable differences, nor differences in benchmarks (the thread warned not to expect any)
I can't really say I've noticed much slowdown in the phone after encryption though. I don't do much on the device that's very processor or storage intensive anyway. It's mostly email, forum reading, a game of angry birds on the plane, and Need For Speed Hot Pursuit. I use SetCPU to keep it underclocked to 1000mhz when on battery with the hotplug governor (done wonders for the battery life), and even with that I haven't noticed a seat of the pants slowdown. I'd be interested to find out if our processors include a native AES instruction set or something similar to the newer Intel Core series processors that offloads some of the work of encryption and decryption. I don't have any before screenshots from Quadrant, but an after is attached. Anyone else notice a similar change?