Are Hyper-V IDE and SCSI devices performance equal

I've found that the disk is usually the biggest bottleneck for our virtual machines. Especially if you're doing continuous integration across multiple VMs, you'll be doing a lot of reading and writing. If all the CI processes start at the same time, the problem is compounded.

The quickest way to get better performance may be to add physical drives and distribute your VMs across those drives.

Another way to get better performance would be a large RAID5 array. We've seen amazing performance in large VM clusters when you have lots of drives to spread the data across.

Serial Port: Yes, but you have to set up the COM as a Named Pipe on the host machine, so I don't know how this will affect your software.

Tape drives have been discussed here and the answer is an emphatical "no". You best bet is to install the tape drive into normal server (if your host machine is the bare-metal Hyper-V this won't work, it has to be the normal Windows install, and then have the Hyper-V role added) and expose it via iSCSI. There's plenty of software around that can do this. Starwind is one of them.

As for the fax card, I haven't seen any sort of PCI pass-through in Hyper-V. VMWare ESXi is way ahead of Microsoft Hyper-V on this front, however to use PCI Passthrough in VMWare you need to have fully supported hardware which may pose an issue if you've already purchased the servers, and there's no way to know for sure that your software will work the way you expect without trying it.