He coul´d run wow in background, while botting. Or just max one Session (window/fullscreen). Three sessions is easy doable. Anyway. WoW is CPU heavy not GPU. I don´t think its a good idea to put extra load on CPU as HB is CPU heavy as well.
Have an AMD 290 OC with three 80mm Fans and manually set the fans to 25%. The card heats up to 85 Celsius while running Ultra, but thats not off limits, so it´s ok for me. CPU is limited to 4,5 GHz, fast enough and cooling system can handle this.
(5 Sessions, but normal Graphic Quality is set to medium, don´t need the quality while botting dungeons eh? but forgotten to go down from Ultra sometimes so I know its ok with Ultra, but feel better with medium)