What I got told was that 2 gives more revs and is for dry conditions and 1 gives less revs and is for wet conditions
But it does not make a difference in my opinion
i have a mich x-light on the rear and is ste best gripping tyre i have ever felt dont know wether the x11 is the same bit can grip on any thing and had no problem with it coming off the rim i have it at 3-4 psi
the 2009 beta is known for having cracked frame and swinging arms and snapping of the radiator filler neck the 2010 have solved this problem by moving the neck and stronger welds so the frames don't crack and the 250 is the better option because it will go up all the things the 290 dose and the 290 is a bit snatchy where the 250 is smooth