I don't think it's worth the extra no. It is clocked slightly higher but the frozer III will match that if you use MSI afterburner to OC it. The frozer IV may OC better but if you are going to Xfire at some point due to the size of the case I would leave them at stock speed to help keep temps down and power requirement.
650W was recommended for Sandybridge and the 6950, seeing as Ivybridge and the 7850 both require less power then 650W would most certainly be playing it safe.
I don't understand why you are asking me to question myself? I wouldn't spec the kit if I didn't think it was suitable lol I try my best to spec stuff that is firstly in stock, secondly at the best price (and warranty included) giving the features wanted/needed and thirdly i do try to keep it all looking tidy together.
Waiting has quite frankly screwed you over, this weeks deals aren't as good. If you are desperate to get stuck in you could order the case and PSU now. You can testfire the PSU with "the paperclip test" (google it) to make sure it starts up, then fit it and tidy the cables together nicely in the case, ready for the mobo bundle and extras. Maybe next weeks offers will be kinder.
RAM you don't need faster than 1600Mhz really, you're supposed to want the CAS to be low as possible. Technically PC3-12800C9 is better than PC3-12800C11 (lower CAS is better) but in the realworld you won't really notice the difference. We usually spec lowprofile height RAM so aftermarket air coolers can easily fit over them. Some RAM has aggressive styled heatsinks, it's ok to use this with stock coolers and closed loop liquid coolers if that's a look you want to go for.
The beauty of building yourself is that you can choose what you want and how it looks, making it more your own than an off the shelf job anyone can buy. I have a feeling your friend might get quite envious of your build, for £800ish I can give plenty of examples with different styling and features.....it's what you like that counts.
I notice you have taken the DVD drive off the spec sheet, if you are intending on reusing one have you checked it's sata?