I realize that, but i already said that ignoring the fact that 750w isn't necessary, you may have a harder time with finding a good 600w PSU with 4 6 pin connectors. The 660TI uses 2 each. All of the 600-650w PSU's either:
-Only have 2-3 6 pin connectiors
-Are more expensive or the same price as the 750
-from very questionable brands (only 1-2 are in this category)
Judging by that, wouldn't you agree to get the 750 from a good brand and product line for the same price?
Not really, since I think SLI is pretty silly anyway, some games having problems with the second card and having to reduce to one anyway. In a single monitor 1080p setup there is no need for SLI at all, so no reason for a big 750. It's not really future-proofing much as by the time he would need a second card he could just upgrade to a 760/770 or whatever is out at the moment that is a good deal. Why spend the extra now for a large PSU when you can save that and put it towards a better GPU later when your gonna need to upgrade anyway that will work with the smaller PSU?
To say corsair is a good brand is a fair call, but to call the cx series a good product line is a bit far fetched.
When there are so many decent alternatives around at the 600w range that will do the job in a very respectable manner there isn't much point looking at a 750w psu unless your a silent freak and never want to risk having your psu fans crank up a bit.