Upgrade Path for my 'Project' Computer

I have a Late 2011 Macbook Pro, my setup follows:

Late 2011 Macbook Pro

Intel Core i7 @ 2.2GHz

AMD Radeon HD 6750M, Intel HD Graphics 3000 512MB

12GB Kingston 1333MHz DDR3 RAM (4x1,8x1)

128GB SSD Startup Drive

Original 5400 RPM 500GB Hard Drive relocated to Optibay

Battery Replaced Last October

So, I bought this computer for $500 off Craigslist. It isn't the top of the line from 2011, but it is fairly quick. However, I'm building a Gaming PC and I replaced upgraded all my parts in this Mac myself, so I'm very confident in my computer skills. I'm not interested in buying a new Mac Laptop, due to the fact that they are not upgradeable. To replace this laptop with a laptop to fit my needs, it would cost me almost the very best of the 2016 lineup, about $3,000.

I know many people say buy a new one, but I want to upgrade to the best processor for this computer. The question I have is, when I do this, can I use a 2012 MOBO or just use the better 2.5GHz board from 2011? Can the same be done with the Graphics Card, upgrading via a Motherboard swap?

Thanks