I think the 800D is the best. Lots of room and cables management.
Years ago, I'd have said the same thing; I had one of the biggest towers on the market in the late 90's (AOpen HX-08).
Now I know the drawbacks as well --huge, heavy, difficult to transport to LAN parties, etc. I also like the SATA dock of the 650D. I don't need more than 2-3 hard drives; I have a server keeping track of my important data. As cool as the hotswap feature of the 800D is, I also don't need it; again, I'm covered by my server. The 800D is also significantly higher in price.
There are pros and cons to both the 800D, 600T, and 650D. However, I think the 600T/650D are reasonably large cases as it is, and I'm satisfied with their cable management and the amount of room they offer. I'm also more comfortable with the lesser impact to my overal hardware budget.