By the time I get round to visiting a shop I usually know from research what I want anyway, then it's simply a case of is right for me. The other main thing with me is that I'm 6' 5", so I pretty much know that the largest frame they do is the one I need! There are exceptions, but more often than not it's how it is. I sometimes have to tweak stem length as the like, but other than that if it fits, if it feels right and if I like it that's enough for me. May not be technical, may not be correct, but I've never bought a duffer yet.
I'd agree to a difference between Tiagra and 105, but after that the boundries get inreasingly blurred IME. Tiagra is bascially the best of the budget groupsets, whereas 105 is the lowest of the top end ones. That said 105 is great kit, and I'd go for it over Tiagra every time. I've had 105, Ultegra and DA, and in their current versions I've felt very little difference TBH. Now I had DA on a 2006 Trek Madone, and that was sublime, but I find the current DA to be much closer to Ultegra than it ever used to be.
It sounds to me like your heart wants the Bianchi, and perhaps your head wants the Cube. I can't give you the answer to tat one I'm afraid. There is nothing wrong with buying a bike with your heart - as long as it suits your needs, fits you right and gives you confidence to ride it well. You need to go and get sat on some bikes IMO. You may find the Bianchi just doesn't feel right when you sit on it, and the Cube may feel perfect. Then again you may see something comepletely different.
I don't rate
Halfords at all, but the Boardman bikes get very good reviews, a lot of CC'ers have them and are very happy, so that could be another option. Also Focus bikes, they have always offered great value for money. I bought a Focus Cayo Pro a few years ago. It had full Dura-Ace and cost me £2200. If it had been a Scott, Specialized, Giant or any other big name I wouldn't have any change from £3000!
All I'd say if buy the best spec you can, this will help avoid, (or at least delay) upgrade costs if you get severely infected by the virus that is cycling. On the other hand, if you have no desire to upgrade then Tiagra components will be cheaper to replace than 105 and are entirely functional and used happily by 1000's of cyclists every day. Then again, by the time you may need anything in the way of replacement parts or upgrades you can usually pick up new old stock cheaply anyway
