I would also advocate a 90 gallon if you can spare a few more bucks. You'll like it a lot better, they have the same width and depth but are much taller. The water will stay cleaner.
I don't really advocate 3 oscars in a 90 gallon but I feel it is possible. 100+ gallons is more preferable but the 90 was the best I could do and they're growing really nice and have all reach 7+ inches in less than a year.
A convict trio has made a good addition to my tank, if you want my personal opinion. They can reach about five inches and have attitude to match the oscars. I'd suggest 2 females and a male. I have two males and a female and even though the tank is large they still sometimes fight over her.
If you got the trio and a 90 gallon, you'd have my setup minus one oscar ;P I have a gravel bottom though.