05 ST3 owner
860GT said it IMO:
The better suspension of the 4S, or the 3S over the ST3, is the way to go.
At the end of the day, better suspension gives more in most curves then extra grunt, but no doubt many will differ.
I am very happy with my ST3, however I have recently fitted a fully adjustable Wilbers rear shock (Ohlins quality, cheaper price) and I am going the 748/916 fully adjustable route for the front forks. I thought the rear suspension was pretty good before I upgraded, but the extra suspension performance is noticeable. Similarly the front rides well and only occasionally tops out.
On the same day I rode a Multistrada, Aprilia Shiver and ST4S along the same road. The Titanium Nitride coating on the ST4S Showa front-end really made for a smoother rode over a bumpy surface. I liked the 4S best of all but it was too expensive for my budget. If you can get a 3S choose it over the ST3, and likewise a 4S.
The 4S motor had plenty of mid-range torque and I didn't have the opportunity to wind it out. I miss the sheer power of my Triumph 1050 Sprint ST, but the ST3 has plenty of real road performance and is a fine bike. I changed fro the Triumph for the V-twin charisma of the Duke.
To close, I have had absolutely no complaints about power delivery or fuelling on my 05 bike.