You've got 8 troop slots right? fill four of 'em up with grey knights, and four with stormies armed to the teeth with anti-tank guns. If you feel the need, mount some of your stormies in chimeras, for the multilaser and lasguns. Then, max out your fast attack with drop troop grey knights, and for any inquisitors you take, mount them in land raiders, further increasing your anti-tank potential. Take an inq. lord and a grey knights master, so you can take dreads and HS land raiders. Then, take an orbital strike, and choose whether you want 2 land raiders, 2 dreads, or one of each. I would ignore the termies, as they're just grey knights with a +2 save. Take an assasin, 2 inquisitors, and trick out the retinues with antitank power, plasma cannons, multi-meltas and such. Do the same with the inquisitor lord.
Also, stick a HK missle on all vehicles that can take 'em. Unlimited
range krak missile my friend.
There, a list with so much anti-tank firepower a titan would think twice!