Upgrade advice - Lightroom and some gaming

Approximate Purchase Date: Before Christmas, sooner the better

Budget Range: (e.g.: 300-400) : Variable. Want somewhat good performance at prices that makes sense for my needs. The upgrade must also be "noticeable" otherwise I could also just fix my current problem. Therefore, I'm guessing around 400-500$

System Usage from Most to Least Important:
Adobe Lightroom ( and sometimes Photoshop )
Gaming

Are you buying a monitor: No

Parts to Upgrade: (e.g.: CPU, mobo, RAM) **Include Power Supply Make & Model If Re-using**

Parts to upgrade :
Intel I5-750
Asus Maximus III Gene (microATX)
4x2Go G.Skill Ripjaws 1600Mhz

Parts to ideally reuse :
CoolerMaster Hyper 212 plus ( if possible )
120 Go SSD
500 Go HDD
Seasonic X-650 PSU
ATI XFX 5850
Antec Mini P180 case ( microATX only )
Dell Ultrasharp 1680x1050 monitor

Do you need to buy OS:
I bought a "Windows 7 for system builder" back then. My guess is that I will have to buy a new one but I'll try moving it stating that my motherboard is dying. Let me know if I have a chance..

Preferred Website(s) for Parts: Canadian sites like NCIX.ca, Newegg.ca, BestDirect.ca

Location: Quebec, Canada

Parts Preferences: Prefer Intel cpu

Overclocking: Only if needed down the road

SLI or Crossfire: No

Your Monitor Resolution: 1680x1050

Additional Comments: I prefer quiet PCs. Not really a big factor for this upgrade.

And Most Importantly, Why Are You Upgrading:

After 2.5 years, I suspect motherboard capacitors... Nothing overclocked, blue screen on cold boot, tested all ram successfully. Sometimes blue screen for no reason simply browsing. Never been unstable before this summer.

Wife will be upgrading her camera to a Nikon D800. 50-60 Mo Raw files are longer to process in Adobe Lightroom / Photoshop and would like to futureproof.

Would like to be able to play GuildWars 2 and some upcoming game. I will upgrade my Ati 5850 down the road, but not this time unless really needed.

Thanks for the help!