Road bike recommendations

I'd go for the Ultegra equipped version but it's £300 more than the 105, and personally, the 105 is pretty good as it is, especially when it's £115 more than a Tiagra equipped one (whom I really disliked the brake shifter).

I like Ultegra. It might seem expensive next to 105, but it's a bargain compared to DA. Spending money on the parts that last (everything except the chain and cassette really) is a good investment.

mix and match is always good providing it work well with each other, e.g. 10spd 105 derailleur with 8 speed cassette.

Why? So you feel like you invented your bicycle?

Perhaps put canti-mounts on it?