This is the wrong comparison, and anyone who is trying to sell you something based on this comparison is playing slimey games and should know it.

CGI/Apache is comparable to and should be compared to CGI with IIS. Because process startup is so heavy on NT, IIS generally loses this.

Now if you want to compare IIS running ASP with something, you should compare it with mod_perl. Performancewise if you have reasonable hardware you are limited by your connection to the internet, so performance is not an issue. Apache wins on stability, flexibility, portability, support and price. Which might just have something to do with why Apache is the market leader and IIS - despite having one heck of a marketing budget behind it - is not...