I use the 2600K rig at 4.2Ghz, in Vegas 11 for my videos. I run HT on, and I can encode stuff pretty fast. I don't have any figures, or way to compare it, but safe to say I can play back 1080p50 footage in real time without any stuttering at full resolution (from AVCHD, so the CPU needs to "uncompress" it. I run offset of -0.25V, which means I have a lot of headroom on my CPU, which IMO I don't need.
My gut instinct says that 5x1080P monitors on a single 7970 will be fine for lower detail games, or for older games/ windows usage. I barely get 60FPS with my HD5850 at 2560x1440 in WoW for example. I realise how intensive stuff is, especially when you reach the higher levels of resolution.
The 4TB drives are also very expensive now, may be best to run 2x2TB drives, unless you require all eggs in 1 basket
Of course this is all IMO, but I already have the benefit of knowing how far my lightly overclocked 2600K rig gets me, which is safe to say, I never wait for it to do anything, some more FPS in WoW would be nice, but don't see it drop below 40 anyway. Video encoding/ editing is quite fluid. You always have Quicksync if you go with an Intel CPU with HD graphics and Z68/Z77 motherboard, that allows for accelerated video encoding with programs that support it