Def. buy the 4000T. More expansion, better air-flow..etc. as things do heat up once you put your toaster + flyer and any other cards you might want to add.
I had a 4000D once and I wanted to put a CD rom drive in and man is it tight against the PS. I did not like it, although Im sure it would have been fine..but thats just me I like things to be perfect.
Dont settle for the 4000D.. get the 4000T :-)..plus the resale value in the future if it ever comes to that.. :-).
Rich
ny