This looks like a very interesting project. To be honest though, I don't think a hacked up version of the ring lockscreen will go any faster on sense 2.1 roms.
If you check out any pure Sense 3 port you will see that the lockscreen is way smoother than any 2.1/3.0 hybrid or even a 3.5 rom, even with all the resizing.
In my opinion it all comes down to framework changes between sense versions.
But anyway, I guess a good starting point would be a smali by smali compare between an original sense3 htclockscreen.apk and one from the hybrid roms to roughly see what needs changing. Then you could try to apply the same modifications in the 3.5 lockscreen apk.
HTC Desire PVT4 AMOLED
Google Nexus 5