Upgrading PC

[Slyminxy]

I'll just hijack this thread for my own ends.

My current gaming rig, that supports up to 8 clients (or did..
..because around 2013/2014 new year line, I started having weird blue screens , right after I updated the GFX drivers.
Going back to previous version didn't provide a solution, so I went to Asus's drivers (the gfx was manufactured by asus) and it doesn't crash anymore for the most part.
RAM sticks are fine, so are the hard drives. There's nothing physically seen on the motherboard or the GFX, tested everything multiple times with multiple tools, together and separate. No errors evident.

One of the most common bluescreens happened after I tried to open a can in space. Or had more than just my own clients in the same fleet.
Each client is run from their own folder on the hard drive.)

Rig:

Q9650 CPU
GA-EP43-DS3L motherboard
8 GB of RAM (4x 2GB) DDR2 1066MHz
Radeon HD 7870 2GB

Hard drives are currently separate 250GB for system, 320GB for Games and 5+ HDD's of 500-1000GB for other stuff.
Running Windows 7 Professional SP1 64bit

So, I was thinking. If I upgrade to anything lower than a 6-core i-7, how much do I actually gain? I'm already running 4 cores. The cache is also 12MB on those Quad cores, so I was thinking first upgrade should be going to an SSD drive for the system and games partitions and maybe going to 4x4GB of ram sticks.

The budget, if I decide for a new machine (CPU, MB, Ram, SSD x2, PSU) is around.. 900€. Any hints?