Funny but that card isnt even on BLIZZARDS compatibility list, dont post false info please..
You are acting as if there is something special about the cards on the list. They are video cards from Nvidia and AMD. They are all designed the same. The fact that a card does not appear on a list from Blizzard simply means that it is newer than the list, or they never bothered to test it. Since the GTX 680 is also not on the list, do you assume it will not work as well?
What actual benchmarks I can find have the GT 545 about even with a 5670. It is not clear if that is the GDDR3 or GDDR5 version. Note that the linked card is a GDDR3 type and so will have lower performance.http://community.futuremark.com/hardware/gpu/NVIDIA+GeForce+GT+545/compare
So running D3 adequately is very much likely.
The power draws for GT 545 are fairly high thoughhttp://forums.atomicmpc.com.au/index.php?showtopic=264
6670 would be the safer course, and it also scores better in futuremark, and is likely better in most or all games. It still has a max draw of about 70W I think... hopefully the PSU will handle it.