Just thought I would add my results to this. I was having performance issues with Microserver, although apparently not as severe as some of you were having. I decided to run a basic benchmark before and after changing the drivers. Results were quite dramatic and I could tell as soon as I booted the VM that the performance had changed.
I ran Crystal Disk Mark (all default settings) and the output is as follows:
ESXi 5.5.0 U3a
Before (v100 drivers):
After (v88 drivers):
Don't really understand the significance of the numbers that Crystal Disk Produces, but the numbers seem a lot higher!
Thanks for the help all.