I have a queen conch that I absolutely love. We've had her for about 4 months and she has grown about an inch. I think. The new growth on her shell is about an inch out from the older so I'll assume. I can't tell that she's gotten any bigger, but thats just because I look at her every day
. Over all she is probably about 4 inches. She will definitely be the reason that I upgrade to a larger tank.
We did at one point have a large electric blue hermit & the first night that we put "Queenie" in the tank, he did try to attack her & take her shell, but with the jumping & the slime, the hermit wasn't successful. But it really did scare the daylights out of me. Needless to say, no more hermit.
I absolutely love having a queen conch. I don't think I would recommend her to anyone that doesn't have a large tank, but other than that, she's everything that I could expect from a snail. My sand is gorgeous now that she is in the tank, and she will even eat off of the rocks sometimes. Best of luck with yours, hope that gives you a little more insight!