Taking a stand

I have been hosting a Windows Server 2003 system running as a virtual machine on KVM. On the Windows system is run a .NET app with mysql backend. The .NET app is said to use threads heavily. The .NET app is having problems handling service requests in https. It is slow and drops connections even with minor load. The problem I have with it is that the developers of the app say that I am using a crappy Open Source virtual machine and not some "professional tool" like HyperV or VMware. :-)

Can anyone say here, could the above, what tialaramex described, have effects on KVM too ie. although there is a Windows system doing the threading and signaling "the right way", the VM hosting Linux kernel could have effect to native .NET runtime? Should I quote these comments from here and ask the same on KVM-devel list?