As far as the base Boxster, here's a few videos showing performance comparisons (in case you haven't seen them already). I think that they'll give you a pretty good idea of where the 2.5 and 2.7 base 986's stand.
Motorweek test of the Boxster 2.5, a Z3 and a Mercedes SLK
One of the Japanese Tsukuba races with a Boxster 2.7 versus an Acura Integra R, an S2000, an MR-S (breathed on MR-2?), etc.
And finally, an
overmatched Boxster 2.7 versus a 350Z, another Honda S2000 and a BMW M3, where the Boxster gives away 30 hp to the S2000, 60 HP to the M3 and 123 HP
to the M3 . The Boxster has a Power/weight ratio of 6.09 (KG/HP), while the 350Z has a ratio of 5.01, The S2000 of 5.00 and the M3 4.33. To be honest, a Boxster S (ratio of 5.19) would have been a better vehicle for this comparison
**.
But anyhow, guess who doesn't win this last competition?
