I've done some formal and informal research, and I can say this much for sure, you can't go wrong with the price and function of the Vortex Optics Strike Eagle line, 6X or 8X (my first choice since I like their BDC3 reticle best), or the Primary Arms lines. The 6X may be a litter further away but the clarity at max should likely be a smidge better, but even with an 8x they are very good for the cost of the glass, If I got something very long range (like 6.5Creed or 7mm RemMag) I might consider a 10x for it. Many would say those brands are the value proposition brands of the glass market, and while some will poopoo them, they are glass snobs with more money than sense. You can find some bigger names with great glass that are more expensive for the same magnification and focal plane, but I haven't seen a credible source claim it was a deal breaker or a huge game changer, just maybe the name and marginally better glass (yes, I'm looking at you Tijicon, Sig Sauer, and EOTech). I refuse to put glass on a rifle that costs as much (or a good bit more) than the rifle itself, and the target above was on a poors PSA running Magtech, PMC is also very accurate I find. USMC standard during my time was irons at 5 football fields, and we did fine if we could shoot at all, even with the best glass and rifles, if you don't know the basics and have a lot of practice, the top-a-da-line gear won't make you a good shot. That being said, mine is actually a couple years old (1x8x24 SFP, but the FFP scopes are now very reasonably priced and I would consider one), but you still can't go wrong going to Optics Planet and waiting for the deal/sale, usually you can get the scope and a nice set of rings for free with it. If I were to look for another right now and I can get the SFP with rings for $399 or less, I'd probably pick up another, but my 7.62x51 is my only long range reach out an touch someone cartridge, though I do want to add a 5.56 to the stable sometime. I am all about the low price classics that are cheap and abundant and have been doing the job for decades (308 is STILL a highly used sniper round for LEO and military), no expensive wildcats for me thanks.
Any questions let me know.
IMHO/YMMV