Asking for another's opinion on shock performance is tough because ride quality (as opposed to handling) is quite subjective. There are tradeoffs in any shock selection. However, the question on shock selection is further complicated by the risk for problems and your tolerance for risk. This summarizes the big 3 shock options. Search for more details. Also keep in mind that these shocks will feel different depending if you have sport or comfort seats.
The Boge sport's represent a good combination of performance and ride quality. They are the lowest cost option and have a reasonable lifespan with no known reliability issues.
The Koni yellows represent a good combination of improved performance, excellent lifespan and with a slight reduction in ride quality but at a higher cost.
The Koni FSD's represent a good combination of improved performance with good ride quality but at higher cost and with some risk for a shortened lifespan (search for details).
Bilstein HD's represent a combination of improved performance, exceptional lifespan with some reduction in ride quality but at a higher cost and with some risk for problems (search clunking).
Bilstein Sports give greatly improved performance with exceptional lifespan but with a even bigger reduction in ride quality at a higher cost.
I personally stayed with Boge's because ride quality was most important and my concerns with some of the problems associated with HDs and FSDs. Skip the springs since you are already a bit lower than stock. A shorter spring will need to be a stiffer spring in order to avoid bottoming out due to the shorter travel length so the ride quality will be noticeably degraded. If you simply want to improve handling, get an M5 rear sway bar and you will get flatter cornering with no compromise in ride quality.