Hello guys, I'm thinking of upgrading my desktop after I'm done with my major examinations and before I have to enlist in my country's military (its compulsory, but pretty safe and its only 2 years). I'm thinking of playing Battlefield 3 and Skyrim on as high a setting I can manage, so I was wondering about some upgrade options. As of now, all that is left is me battling with my self control over how much I spend

1st off, I NEED to change the GPU, its an Nvidia FX540 (as far as I can recall at this moment). The computer was my sisters' and she's an architect, but I inherited it. I was thinking of going for Nvidia and also thinking of splurging a bit. So, the cheapest card I would go for would be a GTX560ti, but the greedy elitist part of me wants a GTX580. The real question is, how much difference can I expect between the 2? Or should I go for the middle ground (GTX570)? I can afford the 580, but I wonder if its actually worth it.

Number 2 on the list would be regarding my CPU. The computer has a core 2 quad q9550, would upgrading to a... say i5 2500k be worth it? If I do upgrade, I'll have to get another motherboard and stuff, but I've expected it and saved enough. Any thoughts on the performance difference? That being said, my self-control is being stretched to the limit by my desire to just say "to hell with it" and do a full system upgrade. The rest of the parts aren't great and I may have to replace my 450W PSU, but I still want enough capital to test out a SSD.

Any input would be great. Thanks.