Jimmy Anderson was never an out and out quick bowler. Being a quick bowler isn't necessary to being a good seamer. McGrath + Jimmy, relied on seam and bounce, and swing respectively. Not pace. Pace is far from everything, case in point Australia's Shaun Tait. Probably the fastest bowler since Shoaib Akhtar and he was pretty mediocre. Why? Because he had terrible accuracy and consistency. Consistency, control and subtle variation are the key to test bowling and it's exactly why Anderson and McGrath were so successful. Pace is not particularly relevant.