With my fairly modified 930 I found the biggest limiting factor was the suspension. I went with the RSR coilover kit and it made a world of difference. I haven't run across much that I haven't been able to keep up with and pass at DE events (obviously individual drivers are the greatest variable in any such equation). Really is great fun to lap 996s in an 18 year old car.
'88 Blk/Blk 930 ('Lucy') - Not Stock & Not Running