I'm assuming a 970 will run a dk2 quite nicely?
i would expect so yeah, ATW added into the launch rift runtime (1.3) has really improved performance in games because you do not notice framerate dips so much any more.
if you upgrade to a VIVE I am not so sure but even the CV1 rift i think will be mostly fine with the GTX970. They tend to overclock really well too.
if you do not manage to get your mates, keep an eye on the classifieds (sod ebay)......... i reckon the prices of 2nd hand 970s (and 980s to a lesser extent) will tank once the GTX1070 comes out.
I generally buy 2nd hand stuff from avforums.com classifieds, you need to post and be a member for a few weeks before you get access i think, but it is a fairly safe environment to buy 2nd hand esp if you buy from regulars with good rep
(i have even been given free stuff from there - MGS V the week after launch can you believe it!!!)