Am getting the Pentium G630 and need a mobo to go with. The build will be for cubase use and games. I live in UK, and am thinking about the GIGABYTE GA-B75M-D3H which is £52.79 at the moment from aria.co.uk.
Is this motherboard overkill for my needs? There are cheaper ones. I think the main selling points are PCI-E 3, but not sure thats relevant for me.
I was thinking about getting a GTX 650 or a HD7850 GPU to go with this set up for games like Guild Wars II or Battlefield 3.
The motherboard would be good for you. Having an extra PCI-E slot is always good for upgrading headroom. There won't be much bottleneck on your CPU, but it all depends on the game. It may bottleneck a little in Battlefield 3, but not big to where you notice it. PCI-E 3 is relevant to you. A GTX 650 Ti is a PCI 3.0 Card and so is a 7850. I recommend the GTX 650 Ti because it's better.
PCIe 3.0 is completely irrelevant to you - PCIe 2.0 is still more than enough bandwidth for any video card today, and the Pentium G630 doesn't even have a PCIe 3.0 controller. I don't think any motherboard in that price range is really going to have anything compelling over another (except for extra PCIe slots; not sure whether or not you'd need them), so I'd simply go with what's affordable, like this ASRock H61M-DGS for £39.56 (not sure if that includes VAT or anything like that).
Also, the 650ti is not better than the 7850 by any stretch of the imagination.
The Intel® Pentium™ G630 uses the 2nd generation Intel® Core™ micro-architecture (also known as Sandy Bridge). So it would not support PCI-e 3.0. Even the 3rd generation Intel Core i3's will only support PCI-e 2.0. So a board like the ASRock H61M-DGS would be a nice fit for your needs.