Two opinions.
I have gotten what i feel are pretty good deals on a couple saws off the saw forums lately, so things might just be slow right now.
Others have said there is not much real world performance difference between a 590/600 and a 620. I do not know, but i do know that in my area which is typically devoid of good saws i purchased a very nice lightly used 590 for $200, and there is a dirty 590 for sale at $200 asking that has been on for a couple weeks. Also if a 620 retails at 550, assume everyone on here is like well if i wait for echo day sale, that is 468 before tax or 500 after tax in my state. Yes you are including additional hardware, but there is no longer a warranty. I know personally if it were this close and i was going to buy one i would just go to the dealer to support the dealer and get the warranty.