I do like the look of the 600t case more than the HAF X, but u'd be moving from a full tower to a mid tower, the 600t does support the H100 no prob and same for the 2x 7870s, just a little more cramped, the front panel fan is a 200mm and the h100 would replace the other 200mm. I think u can get a mesh panel to replace the windowed one which has fan mounts to help if heat becomes an issue.
Ah rite ok ! i see that some guys have fitted in a WC kit into this Kit ! how the hell did they do this giving that theirs not much space ?