It is a widely known fact that the least amount twist nessecary to stabilize the bullet the better the accuracy potential. Any time you increase the the spin rate of the bullet the more minor flaws in the bullet become evident in your groups. Granted you dont want to be too slow either. A stability factor should be between 1.2 and 1.5 for optimal results although anything higher than 1.0 is concidered stable. What you dont want is 1.2 when in warm temps and higher altitudes because then at lower altitudes in colder air, you may be running on the line. However in cold dense air, 1.2 is more than acceptable. The 210 VLD in an 11x barrel at sea level in -25 degrees F. will still be stable.
If you think you might ever shoot the 240 SMK, you should go with the 10x. If you know you are going to keep it to 210 grains or less, the 11x will serve you just fine. All other factors being equal the 11x will generate less pressure at equal velocity over a 10x. Also there will be less radial torque during the shot with a slower twist.
Some may argue this point, but there are more benefits to using the right twist for the job than going faster than what is needed. Spinning a bullet faster than needed offers more spin drift, more pressure, more radial torque and less accuracy potential however, in SOME cases can help a bullet pass through the transonic barrier and survive. However, I dont know many hunters who care to hit game with bullets going sub-sonic.
The bottom line is that there will be little difference between the 11x and the 10x as far as the 210 class pills are concerned where the difference between 11x and 9x is getting rediculous.
Pick one and be happy.
