Hmm -- two or three years ago I was there and there was a beautiful GPO which I'm pretty sure was not King Tut. I believe Tintenfisch would know best, she used to work there and I believe stays in touch. Also, did you try their website?
The NEAq generally has a GPO (Enteroctopus dolfleini) and they reach pretty good size. When I was there last November, Sebastian (King Tut's successor) was on his last legs (arms?) and I met his replacement, waiting in the wings, who hadn't been named yet but was already quite large. So... whether you'll see a really old one or quite a young one I'm not sure, but there should definitely be one on display. Find out its name for us if you get the chance. :)
They also go through phases of keeping cuttlefish, and you can almost certainly see chambered nautilus, although this exhibit is very easy to miss - it's 'hidden' (i.e. recessed and quite dark) on the first floor just as you go out to see the seals & sealions.