Hi there. Apple really care about this things. You have to buy a new machine.
Or... check this out: http://browser.primatelabs.com/mac-benchmarks
Do you really think you'll make a quantum leap in speed with a 2010 upgrade?
Maybe you can swap a newest motherboard but not in every model, as far as I read... you can be succesful in a few cases.
The cheapest way to improve your speed is to buy an old Mac Pro with at least 4 cores... (i'm gonna do that...) but yes you won't get portability anymore.
Just check the benchmarks!
That's the same thing I did almost three years ago. I purchased an Early 2009 Quad-Core Mac Pro, bumped up the memory, and installed an un-flashed EVGA GTX 660 in it. I now have an identical Mac Pro with a PCS Radeon 7870 in it. I plan to take it even further once finances allow...
Want portability with a desktop-class OS? Get an old, inexpensive, secondary 13-inch unibody MacBook (Pro) with at least a GeForce 9400M in it, upgrade the RAM to 8GB, and put an SSD in it.
Done.