I rolled back from jb to gingerbread yesterday, running CM 7.2+franco firstname.lastname@example.org Ghz, with a few tweaks mentionned in OP, and I have to say I agree with you all : ICS and JB were not meant to run on our Nexus S.
I mean, with a bit of theming and customization, you have an OS as functional and powerful as Android 4+ is ... and it is blazing fast : no micro lags in transitions, no battery drain ... etc ... no slowdowns when a lot of apps are running on background.
For benchies lovers, I just scored 4700 on Antutu, 2600 on Quadrant and 35 fps in Epic Citadel, that doesn't mean anything, but proves the user experience on gingerbread is far far better than the one I experienced on ICS, and even worse on JB.
Ok, GB stock browser is a really pain is the ass, but using Dolphin ... it's all good.
I love this phone, I love its size and its battery. I have a One X, but with time I find its size way to big in my pocket, and its battery life is .... meh I guess. That's why I use my NS more than my HOX these days (I'm even trying to sell it actually).
Next time I have to switch phones, I'll defintely go for a 4/4.3-inch one, like NS or GS2. And I don't think a quad-core beast with awesome horsepower is required for an average use of a smartphone. I mean, intense web browsing, HD videos, gaming ... that's why N7 is here.
Asus Nexus 7