Is there any advantage to getting a 90gal tank opposed to my 75gal tank i have now ?? The tanks are the same width and length. Of course the 90 is taller and i have 15 more gal of water.

Well, with the additional height of the tank.... will it make it more difficult to clean? It will not matter if you have long arms. ;) Secondly, the advantage ot the fishes is in surface area, rather than depth, so you are actually running more efficiently with the 75 gallon. If you have plants, the light will have to travel further to reach the plants in a taller tank. There's probably more, but those are the first three that come to mind. Reasons to purposely have a taller tank escape me. I rather like the shorter versions. More to aquascape and lower water bill. :D

A 75g is 20" high while a 90g is 24" high which isn't much of a difference. With the larger tank there is more water volume to dilute waste. The taller tank would provide more room for building up the rockwork. FishyFry pretty much sumed up the disadvantages(light penetration, costs, etc).

Good point about more room for the rockword, PB. I have a 30 tall that has taller branches for a natural decor than I would be able to use otherwise.