My burning question is: am I bottle-necking my system at some point in the build? I do intend to overclock my CPU to around 4.2GHz, so I don't want to cheap out on the mobo, and I'm looking for an upgrade / SLi friendly system, hence the 750w. Should I go for a full tower? Do I need to upgrade my heat-sink further? Have I overspent on peripherals? As this is this is my first build, any advice would be greatly appreciated.
excellent choose! don't think about bottlenecking there is no sign,i like your cooler because hyper 212plus are best for sandy series and push cpu to 4.5 or 4.6ghz
gtx 560ti are pretty good for games at maxed.
Oh yes Asrock extreme4 has ample space. It will overshadow your first 2 ram slot but if it is low profile memory you won't have a problem there.
pro-gamer i am sorry about it mate, it is better fitting together and all the parts are going to be on the same technological level while still maintaining the best budget. Also when i propose things to other people i have future-proofing in mind, so that they won't have to go looking to change more than one part to perform a simple upgrade.
on a side note: When building a new rig that costs more than 1000$ you can't leave ssd out of it. Choice one is to get a crucial m4 128 right as you are, Choice two is getting a small 30giga drive and using it as a caching drive on a z68 mobo. I would go for the first even though the second is less pricey.