If you might be tempted to go for a 252 further down the road then that is another argument for a Supercap (preferably DR) for your 282 now. I did exactly this and have gone straight from 282 to 252 and no messing/no loss in trading in HicapDRs. A bit more expensive now but you will save in the long run if you go to a 252 and IMHO the 282 and a SupercapDR are a marriage made in heaven.
Other questions:
200 (non DR for reasons already stated) or 250DR?
XPS2 DR for the 272 now or later?
The decisions depend on 3 things:
How much disposable cash you have now for a system build?
Will you be tempted to go to a 252 in the future?
What sequence of upgrades gives you the best bang for your buck as you go through them?
The last question can only really be answered with some demos, preferably at home with your embryonic system.
Have fun building your new system. It looks like a cracker already and you have some great advice in this thread.