Given the inventory of Porsches in general, you should look for a newer, in terms of engine design, Boxster. At this particular weight, those extra ponies really hit the sweet spot when you are exiting out of corners. It also helps in merging on highways and overtaking soccer mom vans. When I first drove a Honda S2000 on 240 HP (albeit with less torque) and came out of braking I instantly had an 'a ha" momment. Although the S2000 has its engine weight before the front shocks, the principle was similarish to a mid-engine two seater like the Boxster: At 240-260 HP(3.2 Boxster engines), this variety of roadster "comes alive".
280 - 300 (3.4 Boxster engines) give more oomph but the power starts to make more of a difference than the driver. Below 240 (2.7, 2.5 Boxster engines) its all driver.
I think 240-260 is the happy medium. Although if you offered me a Boxster Spyder I wouldn't turn you down.
There are also engine improvements in term of reliablity that come with each step forward in the design evloution. 2.5---->2.7, ----> 3.2,-----> 3.4
p.s.
My Porsche specialists did my IMS and clutch for ~$1800.
This should be the first thing you upgrade on the car in my opinion, even if your clutch is still "50%" so to speak. No point in passing up potential $10+K savings from an engine that didn't grenade just to save $300 (1/2 the cost of clutch).