I dunno, I personally think around 180 is the perfect park ski length for a fully grown, average sized male. I'm 5'9" 160 so about as average as you can get, and the past 3 park skis i have bought have been 180-181. 178 is pretty damn close to 180, ya know? Depending on how they measure, it could actually be 180+. You are pretty tall, but pretty damn skinny I don't think you would want to go any bigger than 180-185 in the park.
I would say that if you like the flex/durability of the Invaders, but just want something a tad more stable the Anthem will be fine.