Re: Best scope for 600 - 1000 yrd comp. shooting
For F-Class which we typically shoot 300, 500, 600, 800,900, 1000 yrds I have two rifles that both wear Nightforce 5.5-22 x 56 NXS - both have the NP-R2 reticals. If you are going to use your rifle /scope for hunting then you may wish to consider the 5.5-22 x 50 with the newer NP-R1 retical and possibly the new zero-stop feature. If not then the 5.5-22 x 56 NXS or even the 8-32 x 56 NXS is hard to beat for competition. I have never actually used anything greater than 22 power; but for F-Class I find this is usually sufficient as mirage can effect the sight picture too much at higher magnifications; there are times when even 22 is too much and you have to wind back. I'm however sure the long range bench rest shooters prefer the higher magnification models.
The things I like about Nightforce is zero adjustment is very simple, 'click' adjustments are very positive, MOA's dialed into the scope do indeed appear to be bang on in the field, and they give years of trouble free service. My oldest NXS is 8 years old. I have owned a few other (cheaper) brands that have disappointed one way or the other; Nightforce never lets you down.
All the best with your decision.