I have both 5.0's and 6.0's now, just got the 6's. The 5's are not thin and under the toes feels like there's something there. Where the toes meet the foot, in that cavity. I didn't like it in the house, but skiing with them it didn't bother me. The thickness of the sock could definitely be an issue if you have a very tight fitting boot.
The 6's are thinner, I like that about them, but they still have the noticable section under the toes. It's better than the 5's but still there. They are not like a super thin ski sock, but definitely like a thin ski sock.