I would go with 6. Depending on how you scape the tank, 3 Sparkling Gouramis in a 10 gallon will look like 3 football players on a football field. Maybe add a Rubberlipped Pleco or a Bamboo Shrimp too!
75g Discus Tank
I would go up to 6.
I have 8 in my 10 gallon, but there are a lot of line of sight blockers and the tank is severely over filtered.