I am going through a similar exercise. Having researched and read many reviews on line, my thoughts were heading towards a mid range Gitzo. However, on visiting one of London's camera shops to see them for real, I realised that I would not be comfortable carring the Gitzo for a day's travelling by tube, bus and on foot. As much as stability is important, a tripod left at home will be no use at all.
The advice I'm giving is that having done some research online, go to a shop and try out the options. I'm glad that I didnt take the plunge after only online research.
My further research is on the Manfrotto 055 and 190 tripods. I will next take my camera and heaviest lens to weigh up my options (kind of literally). I think that after that, the brick and mortar store will deserve my business.
However, the tripod is only the first question. There are a myriad of tripod heads available, and the weight should be allowed for when choosing the tripod. i have found some informative reviews at Cameralabs (e.g. http://www.cameralabs.com/reviews/Manfrotto_190CXPRO3_tripod/ ). I will find out how informative when I buy.
I'm just hoping that I don't change my mind again after making the investment. I may well decide that the extra weight would be worth carrying!
Good luck in your decision making, I will follow this thread with interest.
As much as portability is important, a tripod which is not stable is useless. With high available ISO, image stabilization and lighter cameras, we are able to take many shots today which were not possible a decade ago. Now we need tripods for longer exposures and then stability is very important.