How much higher can you go? I have a couple of suggestions that might push the budget...
Mobo: Get a USB 3/SATA III board. I recommend the Asus P7P55D-E Pro.
RAM: Get some CAS Latency 7 sticks. Newegg (.com) has some Corsair XMS3 sticks that are fairly low priced.
HDD: Samsung Spinpoint F3 500 GB. It should be cheaper, but it's the best drive out there right now.
Other than that, it's pretty good.