HI Aces High, I have used a few companies when purchasing computers, but my last few have been from Cube247. Im not going to list names but other companies i have used have had terrible aftersales.
I have had a couple of gaming computers from them, all really good quality. The last one i purchased was a Perseus system. Its worth looking at their website, however i would also recommend giving them a call as they will spec up a system to meet your requirements.
Let me know how you get on.