What drives are you using and how are they connected to your Mac? Do you have a Kona or similar card/io box? Even if you don’t have a Kona I think you can download their System Test from the AJA site. It measures your drive speed which could be a factor.
Did you update all drivers that might not be happy with SL? Did you Repair Permissions after your installation? Also, it might help to run Disk Warrior. It cleans up your disk directories and that definitely affects performance. You especially need to do this after a major installation.
John
MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.8 QT7.6.4 Kona 3 Dual Cinema 23 ATI Radeon HD 3870, 24″ TV-Logic Monitor, ATTO ExpressSAS R380 RAID Adapter, PDE enclosure with 8-drive 6TB RAID 5
FCS 3 (FCP 7.0.1, Motion 4.0.1, Comp 3.5.1, DVDSP 4.2.2, Color 1.5.1)
Pro Tools HD w SYNC IO & 192 Digital I/O, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN