Having been in a standard GT, standard Glanza, standard SiR Civic, & standard vti Civic. All as a passenger, only driven the Glanza & GT. But in my experiance, standard vs standard i would say the SiR would beat any of the others, not by miles, but reasonably comfortably. But the once you start modifying them, say you spent £1000 on the engine of each, i would say the GT & Glanza would beat the Civics with about the same comfort as the SiR beat the Gt/Glanza standard. I had in my GT a Mani, Decat, Full Exhaust, FMIC, front mount filter & 0.8 bar boost & i could beat my mates 51plate VTI Civic running some kind of air filter (not sure which, not up on Civics) Mani, decat & full exhaust & another mates Civic SiR (same shape as the VTI)running some airfilter & an aftermarket exhaust. The Civics are pretty much even performance wise btw. And Deano im fairly sure your wrong about the LSD comment, im sure my mates with the Civics told me the vti had an LSD as an optional extra but the SiR it was standard issue.
Before buying my GT i was looking at getting an Civic SiR but decided against it as i wanted to modify my car & modifying Civics is to expensive for any real performance gains. Depends what your friend wants, a small, quick, cheap to modify car, or a small, quicker (standard) more expensive car to modify. If they dont wish to modify it too much or atall i would definatly reccomend a SiR.
Long winded and probably worded badly but thats what i have to say lol