May I also suggest Gengar, as it both gives you an immunity to ground and fighting, two of the most prevalent weaknesses on your team. There are lots of set options for Gengar, including LO Sub+Pain Split/3 offensive moves, Black SLudge Sub+Disable, or even Choice Scarf if you want to be super speedy. So while it may not be as fast as all the Pokemon above, I feel it fits your team rather nicely, and only leaves one of your Pokemon (Magnezone), vulnerable to a super effective move (fire).