I own, carry and shoot multiple examples of both the 4506 and 4516, in all their guises and dash numbers. I think my answer would depend on what you want the gun to do?
Carry? Truck gun? Fun range piece? Home defense pistol? While a 4516, in any dash number, is simply a compact 4506, I think for carry by Joe Citizen who isn't kicking doors or storming beaches, a 4516 is a fine compact 45 carry gun. It shoots like a big gun too. Very accurate and reliable.
For a "Truck gun", fun range piece......or even carry, a 4506 is a great 45. It weighs within a few ounces, either way of the vaunted 1911. Not that heavy. Especially with a gunbelt and good holster. And I have a couple of the 4506-1s whose accuracy matches that of my Colt Gold Cup and HK USP. VERY accurate.
$500 in the box is an excellent price for either model. You may find a used 4516 for abit less, but you will be having a REALLY good day if you find a 4506 anywhere for $500 or less.
So, I guess I would get the 4506, for that price, were I you. Good luck with your decision! Let us know which you choose and how it shoots, for you.
Regards 18DAI