i've been thinking the same question [as the OP], for when my stock struts go kaput.
from my reading, it looks like the OE STi struts are overdamped. so on that note: is there some quantitative measure of the damper fluid viscosity/ valve cross-sectional area (i.e. overall damping characteristics) so that one can compare one strut against another? sort of akin to spring rates.
i've walked this path before and usually the results are only marginally better or horrifically worse. i think it's especially true as most STi after-market parts are usually biased toward track applications, with nary a thought to how bad our roads are. not to mention the fact that some people on this forum enjoy being shaken, not stirred.