Variable refresh rate is a technology that makes the monitor refresh whenever the game produces an image instead of trying to match a fixed refresh rate to a variable frame rate. The effect is to make games run more smoothly without requiring any extra performance.
nVidia first introduced the technology under the name G-sync, then AMD pushed to get it included in the DisplayPort standard under the name Adaptive Sync/Freesync. Intel have announced they'll be supporting DisplayPort Adaptive Sync but nVidia have so far remained silent on the issue and still only support their own incompatible G-sync version.
As it doesn't have any drawbacks and is available on monitors from £100 it's well worth considering it if you will be buying a new monitor.
The Corsair 380T is absolutely massive. Four times the size of the SG05 you were considering, and twice the size of smaller Micro ATX cases.
I'd go for something along the lines of this:
http://uk.pcpartpicker.com/p/2rLh6h
You can upgrade to the 380X and Noctua NH-L9i if you want* or put a hard drive or bigger SSD in if you need more storage and it'll come to a similar price as the one you're considering, but it offers a more capable motherboard with extra memory and expansion slots and a smaller case.
*Although XFX cards often aren't the quietest, so I wouldn't bother with a fancy CPU cooler unless you also spend the extra to get the quietest card for your desired GPU. It does put out two or three times the heat of the CPU so it's definitely the priority for cooling in a modern system.