Be sure you are using the latest Fusion Pro 5 which is said to increase 3D performance. Also, you could use bootcamp to run the game natively with amazing performance.
I was surprised that I could run Zoo Tycoon 2 and Lego Star Wars II in Windows 7 through Fusion Pro 5 on my 2012 13-inch MacBook Air 1.8Ghz Core i5, 8GB Ram at FULL speed with all their features turned on! I rember these games running POORLY on a NATIVE PC's in years past! My Virtual machine is Win 7, 4GB Ram, dual core.
PS. I am running the VM from a Kingston 120GB SSD in their included USB 2.0 case. Windows 7 is giving it a score of 7.0! I have ordered a USB 3.0 enclosure from MACSALES.COM, I can only imagine! This SSD is capable of over 500MB/s!