These are gen 2 i7s processors. The other computers I gotta look for, but they are the gen 3s
You would do better to go 3rd or 4th generation i7 processor. If I recall ArrowDirect will just about always put you in a Dell. And while they are not bad machines, there are better options for "gaming" type systems.
Just to check this out spend a little time on Newegg and TigerDirect. I'm not saying you have to buy from these sources but you can see the reviews on their systems more set up to be gaming rigs. You can look over everything from raw parts to build your own up to the complete out of the box ready to go systems. Agreed with others that Alienware products are overpriced for the performance they offer. There are plenty of solid i7 3rd and 4th Gen processors out there where the system itself will be anywhere from $800 to well into the $2000 range. ASUS based systems are great options, and there are plenty of options from ASUS to consider.
It them comes down to the other parts. You mentioned ARMA3. And like GTA5, and BF4, and several others system intensive games the better the video card the better the overall performance.
For these types of games I would be looking at a NVIDIA GeForce GTX 770 2GB or better. That card did the best with ARMA 3 when running the whole thing on "very high" graphics settings across DirectX 11. The older 650s and 500 series all fell below 30 frames per second at some point during testing. Which means lowering resolution settings to hold better frame rates.
Same story on Memory type, speed of, and amount of. You would do better to have 16GB the better speed supported by the motherboard of installed Ram (Memory) for these system intensive games. 8GB is fine, and generally meet the "minimum requirements" but minimum has an impact on game performance. Always has, always will.
To help you out... my gaming PC (which is older.)
I still use a 2nd Generation i7 2600K CPU at 3.40GHz, on an ASUS motherboard, with 16GB, and 64 bit Windows 7 Pro OS. I also have the very GTX 770 2GB video card I talked about above. On ARMA I usually hit roughly 65-70 fps, on BF4 and BFH my fps is well above 100 no matter what is on the screen, on GTA5 I hold their 60 fps max no matter what is on the screen as well. Very rarely does my PC see a performance hit, but I keep up with memory and video card upgrades as needed. I am sure you can see why.
That said, very little on the page you gave us from ArrowDirect will keep up with what I run on a gaming machine that several years old. Why? Video card, memory, and motherboards in those Dells. Again, does not mean they are not good. Just means those systems you quoted us will not have the same performance I get out of a 2nd Gen i7 based rig.