Not much in it - I'd go for the shorter, wider board just for the ease of throwing it around. . . . especially as you're an "average" weight rider.
My Flydoor XL 170x50 doesn't have fins on the toeside - you'll notice if you carve heel to toe that you just fell on your face
you'll get used to it though, and use the edge to carve properly, rather than just leaning on the fins. Very rewarding and a great feeling.
Why not an Oxygen?