They will be exactly the same. That GPU cannot really use the extra ram so I would stick to the evga, life time warranty and a slightly faster chip. In reality you’re looking at a difference of like 1%.
Both cards are around 110watts. The i5 and board will never draw more than 200 watts you have plenty of room. A good quality 400watt would be enough.
As others have mentioned, yes your psu is fine, as for the card the second one seems nicer as you will have GDDR5, and it is from evga, it is clocked a bit faster. What is your budget, maybe you could squeeze in a better card.
The gtx 550ti is newer than the gtx 460 but with your tight budget they are still better than the gts450. If you can, go get the gtx460 as it performs better than the gtx550ti, and it costs more or less $10 more. These cards will allow you to do anything you need, and you can game pretty well on them, maybe not at the highest settings and resolutions but still much better than the gts450.