The Corsair HX850 is one of the best PSUs (10.0 jonnyguru performance rating) on the market .... it has better voltage regulation and lower ripple the the AX 850/860 . The hX750 is untested by jonny which makes side by side comparisons diffiiclt. The HX1000 and HX1050 were rather poor PSUs by comparison w/ 9.0 and 8.5 performance ratings
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=299
The NZXT Hale 82 750 watter scored a relatively poor 8.0 rating ... I'd suggest never getting less than 8.5
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=297
The NZXT Hale 82 850 watter scored a relatively disastrous 7.0 rating
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=274
The NZXT Hale 90 850 watter scored a respectable 9.5 rating
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=199
it's absolute foolishness to judge any PSU by another of the same brand. And while the product line or series is somewhat of a quality indicator, as you can see above, t's never reliable to draw conclusions from one model in a line to another (i.e. HX to HX) ... In other words ...just cause the 850 watts PSU got a 10.0, doesn't mean that a 750 will do as welll....and visa versa.... just cause a 850 got a 7.o, doesn't necessarily mean the 700 is a 7.0 too.
The only PSU I have liked better than the HX850 / Seasonic X-850 is the Antec CP-850 as it had same performance level but was quieter and half the price.
BTW, if ya getting case too.....there are some nice combo discounts with the 500R and other Corsair cases.