I am coming at this from a different angle, probably, but mostly the question I am being asked is if we implement URL Rewrite to handle redirecting older URL's into SharePoint is there a performance hit to our SharePoint 2010 farm? I'm not really sure from a SharePoint view if just checking page load times will suffice, it's what I would check from a regular IIS instance to determine under load if we had a performance problem. Since the question I have to answer is only - will the URL Rewriting cause a problem - I'm not really sure what I could test.
The URL's are basically existing URL's, from the current ASP/IIS site, that will need to redirect to SharePoint url's - getting people from any bookmarked old URL's to the new locations. We only have about 100 of these so it's not an onerous list, but will having URL Rewrite on the Farm mean we will have a performance hit for any requests that do not meet the mapping? I'm a little new to this aspect of SharePoint and URL Rewrite, my belief is that the Mapped URL's are cached and as each request comes in it will be quickly checked then passed on if it doesn't match.