Neither choice is a great track cars out of the box and both need significant upgrades to make them completely track worthy. When comparing the two cars you must also look at model year. Driving a late model Boxster S is very different than a early base model. Not better just different due to weight differences and engine output. For a street car I still prefer post 2002 996 for the mid range torque, style and overall size. If you want a convertible porsche that is suitable for both track and road, out of the box, get a Boxster Spyder.

 

I don't think you'll have any issues. I had a 986 S Anniversary (2004) - same suspension as yours with a little more power. Coming out of a corner, the 911's traction and acceleration is fantastic. I hate to sound like a cliche, but the 911 has soul. In The Boxster S feels a bit clinical, and it runs out of breath just when you don't want it to.

I've been through a few cars in the last several years on my way to owning a 911. There are many who would try to talk me out of the one I've got.

Forget them. The 996 is a great 911. Stock vs. stock, it will leave every prior version in the dust - including some prior turbos. Hell, the beloved 997 is only an evolution of a 996 in the first place.