not too sure what you are saying about 2 cards
I was highlighting how much better that the overall performance of the gtx 550 is and nothing to do with Sli, sorry for the confusion.
You will see a vast improvement in your gaming with the new card and PSU, let us know when the parts arrive and also if we can be of assistance in any way.
If you intend to fit the card and PSU on your own please take the appropriate safety and anti static discharge measures to stay safe and prevent any damage to components, see my canned text below;
The following procedure requires the computer case to be opened so take the following safety precautions 1st, disconnect the power cord from the wall and take anti static precautions before touching anything inside, you can do this by touching a bare metal part of the case.
1: Remove the video card, blow out the slot and then fit the new card securely, do the same cleaning with the Ram slots/sticks.
2: Take the opportunity to clean out any other heat trapping dust, if you use canned compressed air do not allow any fan to spin freely as it may cause damage, hold them still with a Q-tip or clean popsicle stick and do not tip the can upside down as fluid can be emitted when doing so.
3: Make sure that all internal connections are secure before reassembly.TIP:
Make notes of where all the present power leads from the present PSU go to, you could use white sticky tape so that you can write on it then attach it to the appropriate cable and use it for reference later if you are unsure, thats the bonus of a modular PSU you only attach the cables you need to the PSU.