Mac Pro :: Added RAM And Performance Drops In Games?

I bought the vanilla octo-2.8 early 08 Mac Pro back in January. (I've since added in the nVidia 8800GT and a couple 500GB harddrives). As many of you know it's a beautiful machine and I've had very few problems with it. I play World of Warcraft and have recently delved into the world of dual-boxing to take advantage of a triple XP bonus currently available. Running two instances of WoW from separate install locations worked fine. But I found that I was hitting a limit. I couldn't really use iTunes while playing without taking a noticeable hit to the games' performance. So I did the logical thing in this situation: I bought more RAM. Specifically a 2GB kit (KTA-MP800K2/2G) from Kingston.

At first I had them in the wrong configuration. Since the default location for the 2GB that come with the Mac Pro are in slot 1 of each riser, I put the new sticks in slot 2 on each riser. I saw ECC errors and a very odd framerate issue in-game. After about 15 minutes, one instance of WoW would run at 60fps (v-sync is enabled) and the other instance on the secondary monitor would drop to 2-5fps. They would stay like this for about a minute then the framerates would swap: the primary monitor would tank to about 2fps and the secondary would fly up to 60fps. I stopped playing, read up on the RAM placement and found out that the pairs need to be on each riser together. I put the Apple RAM on riser 1 in slots 1 and 2, the Kingston on riser 2, slots 1 and 2. Same story. ECC errors and alternating horrible performance. I then tried swapping the RAM locations and put the Kingston on riser 1, Apple on riser two. I also reset the PRAM as I read that might clear any ECC error issues when installing new RAM. In this setup I had no ECC errors. The framerate issues were still happening though.

At first I thought it was bad RAM. But when placing them on riser 1 I see no errors. My other thoughts are a bad riser board or overheating. Although I've never had heat problems and the RAM seems to work fine if the Kingston in on riser 1.