For anybody that wants to know the answer to this question the answer is it is absolutely fine to stay in the uk for the maximum amount of time. Truth be know, do expect ALOT of questioning, but the absolute most important issue in this is to be totally honest for how long your staying, where your staying, who with and what your intentions are while being there. On my girlfriends first visit to the U.K we made the stupid mistake of flying into the U.K without my fiance having a return ticket NEVER COME WITHOUT A RETURN TICKET, EVER. We sustained substantial questioning and harassment about when she was leaving. At the time we were naive and didnt have a clue about imagration so i argued with the I.O that she was staying for a couple of months but didnt quite know when she'd be going home but it would for sure be before the 6 months was up. She was very skeptical. After around 30 minutes of questioning we did manage to persuade the I.O that she was staying with me and that she had obligations back at home so she would def be returning within a few months. I have NO idea how we managed to pull it off now i look back, but she let my fiance through in the end and stated "The next time you visit your going to need to be ALOT more prepared than you are now, but because i believe this is a case of naievity i am happy to let you through this time but you MUST leave before the 6 months" We were shocked at how serious they took us, but at the time (2 years ago) we were very un-educated about imagration rules.
The second time my fiance came over was for 6 months. And i was worried sick that she would be refused because of the amount of time she was going to be staying. We actually re-hearsed with each other about questions we knew we would be asked and we knew our answers would have to be the same in order to avoid perception ( not that we intended perception in the first place!) We made sure she had plenty of suppourting documents, this included Bank statements showing my fiance had £3,000, wedding invites, information about where she would be staying (with me) a letter from my parents suppourting her visit, Letter from me suppourting her visit, return ticket for the exact date she would be returning (in this case it was just before the 6 months was up). Not only that but we actually interviewed each other so we knew what to expect. I was worried sick she would be refused entry. When she arrived at immagration, she was questioned. She was asked how long she was staying, why, where and all the rest of it. My fiance was totally honest with them, showed them all of her documents proving all the questions aksed. The i.O DID CALL ME when she arrived, he asked me about 6 -7 questions regarding my fiance's visit, i answerd them all with confidence (because we had re-hearsed them so much) This took about 10 mins on the phone and he told me "Ok thank you for your co-operation sir that's excellent, your fiance will be through imagration shortly"
He let her through with no further questioning or hassle, but he did tell her to watch the amount of time she stayed for on her next visit.
The moral of the story is, be truthfull, back yourself up with suppourting evidence, show ties back home and DO NOT come across as your lying. If you do these things, you will be more than fine. Thats our expirience with it all. Obide by the rules, Never lie or decieve and you should be granted entry without major problems. Oh and i know alot of people say I.O's are scary but this guy was actually a nice person so dont be put off, there not all the same !
Hope this helped somewhat!