5
I certainly think that my site is quicker using XOOPS 2.3.x than 2.0.x, but perhaps that's just me looking to rose-tinted glasses
I don't use caching on my modules/blocks because I don't need to.
On the problem sites, is it a particular module or block that's causing the problem, or is it the number of quesries being run to populate the homepage?
With regard to optimising your sites, deleing cache files, etc, I would recommend trying the xoopscare module from
http://xoops.instant-zero.com/ - my site has been running well (I think better!) since installing it.