According to an article on thedctimes.com, Ben Grubbs is ranked in the top 20 of guards in the league. He is ranked number 18 according to this article's somewhat more scientific approach. The article ranks guards based on different parameters, such as pressure rate and snap count. Grubbs has a pressure rate of .89% which means that he allowed quarterback pressure only about 9 times per 1000 snaps. At least, that is the way it is explained in this article. That's only slightly below the level of Carl Nicks, who had a pressure rate of .68%.
In any case, it looks like we have picked up a solid Pro Bowl guard in Ben Grubbs. He did come at a pretty steep price though. I sure hope he fits right in, as management has stated.