Personally I think six weeks is just right. I absolutely hated school and sixth form was only marginally better and looking forward to summer was the only thing that kept me going from the beginning of the spring term to the start of the summer holidays.
Plus, breaking the six weeks into three blocks of two or two blocks of three is worse for both students and teachers I think. Ever since Year 9 or so I've received work every single holiday and half term to do in my own time (which I think most people agree is fairly standard) and three extra holidays would just mean I'm suddenly getting three times the amount of work to do, and teachers are getting three times the amount of marking.
(Edit: Black team)