I moved from Load Runner to Silk Performer and both tools have worked well for me.
The one thing that I think LoadRunner has over Silk Performer is the Analysis portion. You can drill down a lot more with Load Runner. In SilkPerformer you have to build extra timers to drill down and then if you want to drill up you need more timers. Overall the Analysis portion area is a lot easier with Load Runner and that adds a lot of value. Also setting up the server monitoring is easier as well and all in one interface.
Senior IS QA Developer
LR, QTP, QC Admin, Sitescope, SilkPerformer