Well, the 12V rails are rated for 48A and 45A respectively, so it's really not much of a reduction. Either would do fine.
What I don't understand is why you want to buy a new PSU when you already have one that's perfectly fine?
The cooler is fine; a LOT of people have combined the Core i5-3570K and Cooler Master Hyper 212 Evo.
As for the PSU... Either's a good choice to be honest. The 620W might be slightly more prepared for any hardware upgrades, but still it's just 3A more on the 12V rail. The G550 is a newer design and probably a bit higher quality... I suppose I might go for the G550 if I had to choose.