hyper: it was a thread in the forums rather than an article, but I'm not sure where it is at the moment, I'll take a look for you later. I believe it was in the Macro forum section.
Sigma's macro lens isn't the fastest in terms of Auto Focus, but the HSM they have now is pretty darn fast. For macros this isn't the biggest problem. USually you don't use a macro lens for general photography, only for macro, and sometimes for portraiture.
Build quality, that's just ridiculous talk. It has a metal mount, it's solid, what else do they want? Waxed ferarri red with sparkling pearl inlay?
Don't get tricked by people who say build quality sucks. All they look at is how the lens looks from the outside. It has metal mounts, awesome glass, and is solid. The texture isn't smooth like nikon, and it doesn't have some gold plaque on it saying it's a nikon, but really, build quality is not an issue. If these guys went into the lens and found a bunch of loose screws and such, then sure, bad build quality, but if you look at the outside and base your opinion on build quality due to the different textured exterior, I just think that's waaay too superficial, and you may be missing out on a great lens just because of looks. Plus I like the sigma look, it feels really high quality.
Big companies, like nikon, canon, sigma, tokina, tamron, they all have pretty darn good build quality. If you start dipping into the super discount lenses, then you should be a bit wary.
Unless you see people's lenses falling apart without being mishandled, then sure, build quality. But if you're just going by what people see and feel when they hold a lens, that's not the best.
For Fish tanks, however, I may suggest the Nikon 105 with VR. There's always those times when you want to shoot your fish, or you want to handhold your camera. Sometimes you want to go outside and shoot bugs and flowers, but the VR makes a world of a difference =) I don't have a macro VR yet, but damn I can assure you there are plenty of times I wish I had the VR lens =)