Just picked up a 05 s40 T5. 95k on the clock nice clean car. First job on the list is the timing belt. I was looking to do some perfomance upgrades so which performance upgrade should I do first.

 

I'd start with good wheels/tires... Not sure if there are after market sway bars for the 05s but that's a good add without lowering the car. For the drive train, I'd start with considering a transmission flush and upgrade to premium fluids. After that, its about air. Free intake, larger downpipe post turbo are good starts as well. If you decide to go for an ECU recurve, these will help get the most bang for the buck.

 

Timing belt is good to 120k miles.

There are some ECU reprogrammers out there if you have the cash. No experience with one just hearsay.