I'm 5'9", 165lbs (a bit more now), intermediate.
Will Automatic 109 175cm be too short for me.
I have Rossi S3 in 178cm which feels just right for the most part (sometimes too short).
My carving skis are in lower 170s.
Not easy to test them, I'm on the East Coast.
I think I have perfect East Coast quiver (167 Blizzard Slaloms, new 175 Fischer Motive 86, and 178 Rossi S3) but I'll be going to Utah this year (maybe more than once) and feel that I need something wider and stiffer than my S3 but still easy to ski.
get rid of the s3, take the motive and demo some skis in Utah. You are talking 2015 skis that you probably gonna pay full price, there is no reason to skip demo if you are paying full price! Do some demos, store will use the demo money towards the purchase price!
$599 for Automatics 109 - I guess it's full price.
I thought they would be fat enough for my weight as powder skis + OK when snow is less than perfect.
I love to demo skis but not when I fly West - I want to spent that few days on skis I feel comfortable and confident - I remember loosing too much time in the past trying to figure that out while there.
S3 on the other hand I got for half price and really like them for eastern trees.
Will there be too much overlap between S3s and Automatics 109?
I'd say it's better to loose time on demo skis than to end up with the wrong ski. If you are planning on keeping the 3 skis I think it's a waste to buy the Auto 109.
Get something ~115mm to take to trips with your motive if you are able to bring more than one pair.
If you are set on the Auto 109, I'd go 182cm for what you are describing.
I skied several of the fatter Atomics, Alibi, Ritual, Automatic, Bent Chetler, a couple of years ago at Big Sky and the only one I didn't like was the Automatic. I loved the Ritual and Bent Chetlers and bought a pair of Rituals because I thought they would be more useful than the Bent Chetlers. After about mid-January last season, I skied only the Rituals because we had such great snow.
If you haven't skied them, don't buy them. Just demo some skies. If the demo shop isn't right at the base area, just demo a different ski each day. But, if you money to throw away, help yourself.