Frank Goossens on "[Plugin: Autoptimize] cant get it to work - site running 10 times slower"

when CSS optimization enabled, everything getting slow

but only on the first request, as you're using W3TC, no (AO isn't active if a page is served from cache)?

and broke down

have a look at the FAQ and specifically the part about troubleshooting. you might have to exclude some of the CSS from optimization (also for the performance of the 1st page request).

hope this helps,
frank