I'd want to know a couple things - what is the sidecut radius of your Oxygen, and, are you looking to replace it or compliment it? Also, what other boards do you have in your quiver?
At 150lbs, a 1.1m difference in radius might be more significant for you than for me at 175lbs, so I'm hesitant to say which board will be better for you. My "all around" board is my Coiler Safari - 170cm, 14m. When I had my Prior 177, I sometimes felt like the metal said yes and the 11.9m radius said no.
When they leave moguls on both sides of White Heat, or if that, Top Gun, and Right Stuff are icy, the shorter board will be a bit better on those. But for better snow, Obsession and wider cruisers, or if they groom WH wide, the 183 will be better.
But then there's something to be said for shine-ola and having something new. So if the idea of a "previously carved" 177 isn't that appealing, and the 183 in your hands is pretty, maybe just keep it and don't look back...?