I swatched the Cascade 220 Superwash on size 8 needles and got 18 sts at just a smidgen short of 4" and 25 rows to 4". I blocked the swatch and it did indeed 'grow' a bit.
After careful pinning I was able to get 17 sts and 24 rows to 4" as the gauge calls for. If I really wanted to, I could have stretched it a tiny bit bigger - hopefully this won't impact the final product. I'm hoping that if the finished seamed sweater does grow a bit more that I'd like, a quick tumble in the dry will bring it back a bit.
I think I'm going to go ahead and cast on my first piece. If anyone thinks I should go back and re-swatch/use different needles based on what I wrote above please let me know ASAP. I would love any all feedback as this will be my first sweater.
Oh yea - I was too impatient to find a friend to wash and dry it for me so I just blocked it. I'm hoping that it won't make a huge difference..... fingers crossed!