This is not a treatise on scope magnification... obviously would take quite a lengthy tome to go into all the pluses and minuses of requirements for a "1000 yard scope". Just some thoughts on why 10x has often been THOUGHT OF as a "best" for that type of shooting.
10X is certainly not the "best" magnification for a 1000 yard scope. As with most things chosen by the military, 10x was a compromise in a time when technology was not as good as today. 10x offered enough magnification to get to 1000yds (when used by a select, highly trained (at least trained), small, group of shooters known affectionately as snipers) and beyond while experiencing much less mirage effects than higher power magnifications, less training time, less things to go wrong... adequate. Even with today's technology mirage is a problem at and beyond 10x, and there are times the long range shooters with Hubble telescope type optics have to "dial it down" to 10x or less, but with much "tougher" variable scopes out there, it is possible to have the additional magnification for times when mirage is not so bad. So, given all the constraints placed upon the original requirement, 10x became a de facto "best" (if the military is using it, must be the "best"... right???)
Virtually every piece of gear used by the military is produced as the result of "trade studies". Trade studies almost (and that is being generous... I've never seen a trade study produce the "best" of anything) NEVER come up with the "best" of anything. The primary factor is "adequate to do the job within cost constraints". Cost becomes the driver and the original requirement set is often lost due to modifications necessary to fit the cost constraint.
The civilian market is not limited to such trades and if one wants to spend the money, one can go out the purchase the "best" scope on the market for shooting at 1000 yards. $700.00 will purchase a "pretty good" scope for shooting at 1000 yards. The "best" will cost much more and there is some subjective analysis that must be taken into consideration there, as well. Beauty is in the eye of the beholder. The glass quality in the SS10xHD makes up some for having only 10x magnification. I "range" things at 1000+ yards with my 10xHD all the time. If it were 20x+ with good glass, it would be easier, better... 40x, even better... Maybe...