Those are fine for you, I'm 5' 8" 155 and I skied 176s last year and they were fine so 178 should be perfect for you - they may take some getting used to in the beginning but they'll be fine in the long run.
I'm 5'10", and fairly heavy, and 178s are my very upper limit for a park ski.
But then again, I wouldn't have wanted to go down to a 171 in Anthems, so I had no choice really
Sorry for copy and paste but if you do go to that website and pick the ski you want, on the right side of the page will be a little icon that says sizing chart. It is awesome it shows you the length and the corresponding weight and height recommendations. It has a chart for every ski and every length and every brand. Seriously look at it it really helps.