Please note, I just measured the two tanks and updated their dimentions - turns out they're the same size (well, one appear to be 1" taller than the other, but that may just be the framing) - so I'm not sure if they're 90 or 75 gallon.
Quogue, for your purposes, they're at least 20 gallons larger than your 55 - I think 55's are three feet long, right?
Thanks for the offer on the lowland chamber technique! I'd gladdly see what you have to offer - I was just going to build a wood frame cube (maybe tent the roof) and wrap it in clear shower curtain. Not exactly glamorous, but certainly serviceable.