Did you mean Silk Performer? This is something you will need to do on your own. If I provided a complete comparison, it might take weeks. The members here are volunteers. You are asking for a significant amount of volunteer time.
SilkTest is a automated functional testing tool.
LoadRunner is an automated performance testing tool.
As their design and use goals are different, the tools are not directly comparable. The closer complement to SilkTest would be WinRunner or QuickTest Professional from HP. The exact tool of the two might be dictated by the environment you are attempting to assess. LoadRunner is a closer complement to SilkPerformer from Borland.
If you have a question on which tool may be suitable for your environment, you may want to consider a proof of concept deployment against your application in your environment. Work closely with the vendors or a qualified full service VAR for your evaluation. Assuming the evaluation goes well for one (or both) of the tools, you shoulod assume that the VAR or Vendor will be interested in a check for purchase at the end of your efforts. Do not be surprised if they pre-qualify your budget for purchase before committing to a POC deployment.