7mm-300 Win Mag vs. 338 Lapua?

Hey Guys, I'm looking to get my first rifle and I kinda settled my mind already. The problem is that I have limited experience and wanted to get some opinion from people who have first hand knowledge. First I'd like to explain where I'm coming from. I'm 23 and I come from Germany. I've been shooting since I'm 14 and got my owning licences for almost 3 years now. I'm somewhat limited in gun ownership so need to be sure about what I want. I'd like to get a rifle that can do almost everything. Diciplines including: 100m static, 300m static, 500m static, multi distace dynamic, maybe some IPSC. My primary goals are a little bit different though. I also would like to use is for hunting in the future and I really want to tackle the 1000m mark. I found a local gunsmithing company who's making custom ARs only. I haven't talked to them yet because I wanted to get more data. My plan is a lightweight AR-10 pattern rifle with a 16.5" Barrel chambered in 6.5CM. On goes a IOR 2-16x42. My Question is, is that possible? I mean, I did the maths and theoretically it should be. I just want to hear some expert opinions. Thank you guys!

What does everyone think of this cartridg? it very similar to the .300WM but no belt.

Oh lord why didn't I listen! Why did the Steiner have to be out of stock everywhere I looked! I ended up getting a 5-20x50mm Razor HD for $1899.99, what a great deal. Put in on my beautiful newly rebuilt savage 110. XLR chassis, MPA single piece rings, Atlas BT-35 bipod, a smoking hot 29 inch stainless heavy palma barrel, and a camo Cerakote on the whole thing. I get it all together and I am ready to shoot laser beams with this thing. Nope, POI shifts as much as 10 MOA JUST SITTING IN THE CASE. I cant get it zeroed, cant index a FS, cant do anything because of a $1900 POS. I saved my pennies for so long to have a rifle that would make heads turn. I was starting to really reach out there with the range- pushing 1200, 1300 yards and making first round hits- so I wanted to treat myself to something nice after practicing twice a week for almost two years straight. I had my eye on the Steiner T5XI, and they were on sale for like 1300 bucks, but everyone else and their sister saw it too and bought them up quick. I settled... I am sending the scope to vortex today, hopefully I will get one back that works. I was in denial- Couldn't believe the stories were true. I tried everything to correct the problem. Bedded the action into the chassis, unmounted and remounted the optic like ten times. messed with torque and turret caps. Its a crying shame that at 400 yards, I can't hit the target because the scope put my projectile three feet to the right. If they send me a new scope as some attempt to rectify the issue, I am going to the local fudd forums and I am going to sell it for $1500 brand new in the box, and I am going to put my SWFA back on until I can afford something from IOR. at least with SWFA I know damn well I will make a hit whether its rain or shine- I have three of them and they are all reliable. like, go-to-war level reliable. Its sad that a guy can start really feeling confident about LR, and then have a piece of equipment bring him down. I took this scope to my first competitive shoot ever in my life and I didn't hit a single target- put me in last place... I felt like a moron lugging this 28 pound beast of a rifle around like I was some kind of badass and then have my equipment fail on me- totally making me look like an idiot. further more, half of the guys out there had vortex scopes that somehow worked. makes me sick. I am glad you all are here to listen to my angst. sure, I could afford to be a little more humble about the whole thing- and I would be if this wasn't a $1900 mistake. Had Athlon been known to me before hand, I would have went with that.