Mono Issue #1, since the vast vast majority of ASP.Net websites run on windows a Mono performance test even if accurate is going to be of dubious value.
Mono Issue #2, since Mono is nowhere near as polished as the Microsoft .Net implementation the numbers wont really be meaningful.
Windows Issue #1, if you do the test on a different OS than every other test implementation, the results really wont be comparable in any fair way.
Microsoft Issue #1, dont know if it still holds now a days but in past official EULA for .Net prohibited publishing benchmark results. PERIOD.
I am a .net developer and as much as I like ASP.Net I dont think the effort of adding a .Net implementation really would pay off.