Both hardware specs have issues with your stated workload:
- you are not going to run MS SQL server with any kind of performance on only 4GB of memory
- Running two distinct database server systems as well as miscellaneous services on one physical server will quickly run up against resource limits, especially disk I/O
- RAID-5 is not suited for running database servers, period.
- I don't know what you mean by RAID-2, but I doubt you actually meant that
That said, my advice would be to invest in - for now - one huge, capable system and run VMware ESXi on it (this is free)
My personal suggestion on hardware would be something like:
- HP or IBM dual-socket six-core Xeon i7 (12 physical cores)
- 48 GB or more memory, preferably more
- 4x 300GB 15krpm SAS600 disks in RAID-10 for your virtual machines
- 4 or more disks in RAID-10 for your database data
Make sure to put these disks on a good hardware RAID controller (both HP and IBM's built-in offerings are good in this respect)
Combined with VMware ESXi, this setup would allow you to run 10 Windows server VMs easily, with less than 50% CPU load; the system as I specced it is still heavy on CPU, so you could increase performance by merely adding more disks and/or memory to the setup.
The IBM X3650 (which is a 2U box) has 16 (!) 2.5" SAS600 slots available and supports 144GB of registered DDR3 - it is an ideal ESXi system.