Hmm...if it is a gift, then soft mod is out of question...
And like you said he can go either with the 4870/ GTX280/ Quadro FX580
But I am inclined towards the FX580 for obvious reasons...
EDIT: Just saw the edit of wusy...I feel if that soft mod should be easy and if it works good, then he could get the 4870 as he would get a good gaming card as well as when soft modded, a powerful workstation card...