Geophagus Suitabilty

[Barracuda]

I am wondering whether a geophagus would be suitable in my 6 foot tank (however it is slightly slimmer than the norm - it measures only 36cm wide). Will it be suitable with a gravel base? I know there are many varieties of geophagus, so I would want one that would grow no more than 20cm long (otherwise it wont be able to turn!). So what do you guys think? Rio branco? Tapajos?

The main reason why I would like a geophagus is that i thought it would be nice if i had one big "feature" fish amongst the others. (thinking of keeping some angels too)

Thanks!