I'm using an i5-3570K with onboard HD4000 and Musemage which supports OpenCL on GPU. I noticed that with every new driver series performance of Musemage decreases. I guess this is not intended. The ingame benchmark makes it pretty easy to compare.
126.96.36.199.2778 score= 2323
188.8.131.52.2932 score= 2105
184.108.40.20685 score= 1576
As you can see the oldest driver series achieves the best score which looks a bit odd.