As veedubfreak says, the 'C' model supports both DDR2 and DDR3 memory, DDR2 being the current standard. I would just ignore the presence of DDR3 completely, as it will be a long while before its affordable.
That being the major difference between the MoBos, I am not sure how they perform comparatively, but:
1)I have heard people say there are problems with boards that support both
2)People have often recommended the non 'C' model, so presumably its not as simple as a 'something for nothing' scenario
sorry I can't be more help there.
As for the OcUK brand, well its hard to say. The manufacturer seems to have a huge impact upon the overclockability of the memory (correct me if I'm wrong on this, anyone), but there are other reasons:
1) Untried: most people here can vouch for major brands like Crucial
2) Unsupported: both officially (through OcUK, seeing as its a shop, I doubt they have much time for homebrand product support), and unofficially: no one here can help you with any specifics, as no one has used the brand
3)cost! you get what you pay for! (it is a value
brand after all.
4)unreviewed: just about any piece of hardware from any major brand will have comparison review on the internet.
5)compatability: every MoBo comes with a list of supported brands. Now while iit won't be on the list, It might work, but you don't know for sure! And even if it does, the fact that it's not supported means no one has to help you if things don't work!
thread out. Different component, but you can see the kind of difficulties I mean.
So certainly if you plan to overclock (you should!) I wouldn't expect much from the OcUK stuff.
That said, good reviews and all, and I don't want to put you off, these are just my opinions. Sorry if this post is so negative!
Oh as for PSU for the future, unless you are planning on running 2xGeforce 8800GTX in SLI (which you can't do on that motherboard anyway), it should be more than enough. It would prolly be enough to do that too.