Michael,
When I first decided to up grade from stock 19/24 mm TB's for my SC, I believe it was sufficient to have a 21/26 mm combo. It was not too long before I changed to:
21/27 mm
21/28 mm
22/29 mm (this is where I'm now)
All the above had 22/21 mm Carrera sway bars
23/30 mm (spare TB's).
I like the feel of 21/27 or 21/28 for street and track uses. Bigger TB's after these combination seems too harsh for me for street driving. The 22/29 and bigger are definitely more suitable for track driving. And street driving unless you have roads similar to that of the Phoenix area where they have very nice roads. But here in the mid-Atlantic regions, you have to watch out for those bumps and potholes on the roads.
Experience how these different combinations suit your need. Some people have different tolerance and may enjoy driving a 23/30 in town. My two-cents.
Tony