it seems You've done some homework =)
if You need some cpu power & what You get from z77 based platforms is not enough than this road is only solution before jumping on xeons & it offers very good value too. mobo is a bit on a pricy edge, though quite capable & You can stuff up four cards inside!
as for SSD, keep Your eye on upgraded 840 labeled EVO =) might not be in stock yet..
for PSU I would step up to 1200w just incase You would like to slot two more cards later..
as for the case, well personally I don't like it, 'cos it looks like a toy, rather than workstation.
I do preffere clean look /like R4 from fractal-design/, but it's very subjective,isn't it? so.. =)
Overall it's a very nice list of parts & I believe You'll happy with it =)
it's more than capable for Octane.
onemore thing, don't populape all ram slots with cheeper ram modules..incase You would like to double the amount later..so You wouldn't need to throw out 32gbkit..
as for windows, You don't need to specify anything, simply plug Your monitor into lower-end card & beffore rendering uncheck the the box so Octane wouldn't render on 650, that's it =) curently in my temp rig sit 460 for monitor & a bit bigger brother - 670.. works perfect =) W7 doesn't touch it at all before opening OR =)
p.s. since You're looking for Titan, unlikelly You'll top out all 6gb of Vram, so with priority checkbox, taht appeared in Octane not so long ago, You can actually work fluent with one card, so there's not so much of a need for low end card anymore. You can try living without it & save You money..if You see that You don't like smth, You always buy some cheepo anywhere =)