Custom roms for specific use cases I've seen this - Where can I find a good comparison of available custom ROMs?

However the release matrix linked to doesn't really do what it could do.

Is there an objective comparison somewhere that details the ROMs available by feature?

I'd like to find a ROM that's good for battery life and speed. 

The phone model is a Galaxy S I9000.
No one will run the same apps with the same settings in the same environment as you.  Any "objective" evaluation will be no more useful than reading the XDA forums, for example; you're going to end up with an indication of reliability and speed, nothing more.

There's also a ton of ROMs for the SGS, many of which are only published certain places (XDA, MoDaCo, ROM-specific forums).  You'd be hard pressed to find a complete resource.  Even the "ROM Guide" threads on XDA tend to fail to include many of the ROMs from XDA.

In sum, I'd read the XDA Android Development subforum for the i9000 and shortlist a few ROMs that sound good to you, then test them out and see what works best for you.