How to spend money best

So I recently have decided to upgrade my PC, which I literally got from the dump (built it from parts people had thrown away that still work). I don't know the full details of it, but I do know these specs

-intel processor, single core I think, at 1.9GHz

-6gb DDR3 RAM

-win7 premiun 32bit

-Nvida GeForce GT370 (I beleive thats the number) graphics card

So I now have some money to upgrade my PC, but I am not sure how to spend it most effectively. I could probably get about $450 at the moment, but I can't go much about that. I was thinking an i7-4790K, but then I would also need a new motherboard so I wouldnt be able to invest in anything else. However, if spending $450 on the 4790K and a motherboard would get me the biggest upgrade, that's the way to go.

So my question is how can I use my money the most effectively. I run both FSX and X-Plane, but mostly FSX with the PMDG 777, REX4, ASN, and some sceneries. I am also building a 777 overhead panel to work with FSX, if that changes anything.

Cheers,

MD-11Flyer