This was more or less the same problem I had during my MBP dilemma. The MBP, even the Max out model is not a gaming machine. It will game, it can even play GTA V on normal settings a just under 1080p just fine. But its not a gaming machine. That beautiful retina display will only play games at that resolution if they are either older or your willing to play them at 15FPS. Its an almost 3K screen, even desktop class GPU's have a hard time pushing higher settings to screens of that resolution. And viewing them at a lower resolution will look a bit blurry as its not at the screens native resolution.
It will start to come down:
1. Do you need a portable computer to play games at high settings
2. Do you need a Mac (can you get by running windows)
3. Do you mostly play games on your laptop? If so can you live with the settings your playing the games at and the price tag you paid for this computer
4. Is this your only gaming computer, are you willing to buy or already have another gaming computer. Now think back to questions 1.
I had bought and returned 4 computers with these questions plaguing my mind. For me, after 4 different MBP's and 1 super high end gaming laptop my answers looked like this.
1. No but I really feel I should be able to for this price tag
2. I probably could get by but I love the Mac OS and I have years worth of apps and media setups on my Mac
3. No, I really want to but I really only game when I'm at home and I already own a decent rig for games
4. No... I already have one....... ehh, I guess not, but I really wanted it.
LoL, so that's what I had to do for myself. I ended up getting the MBP as I mostly game at home anyway and already have a rig, plus I can still play games when I am out if I really wanted to. Now these may not be the same answers for you so If you find yourself saying I can live without Mac and/or I want a gaming laptop there are plenty of windows laptops out there they have very high end graphics cards that will give desktop like performance.
Running boot camp on your MBP can help. Most games are not optimized for Mac so if you can run it in boot camp it could perform a bit better.
If you want one that is the most MBP looking the RazerBlade QHD has a 14in 4K display and a 970m. It would game very well, its small and lightweight. If you want a beast, the ASUS ROG 17in only has a 1080p display but packs upto a 980m, 24GB ram, 256GB SSD and 1TB 7200RPM (That's the one I had) and will play GTA V at Max settings 60FPS. The Razer will get very hot as its very thin like the MBP but the ASUS run very cool as its thicker and as the best ventilation on any laptop.
Of course if you don't need a portable gaming laptop you could build a desktop that will perform as good as that ASUS for half the price. and that RazerBlade is as expensive as the MBP.
On last note. Please don't ever think you will truly ever game at high settings and not have to plug in. The higher end GPU's take so much power, that if your going to try and play not plugged in it will throttle the GPU. The MBP's GPU does not take that much power so it will perform the same plugged in as not connected. Even though the throttled 970m/980m will be faster than the MBP its going to drain the battery so you will need to keep a charger handy.