In my experience i have found pearls to be very peaceful to each other and my tanks aren't even heavily planted. I have a pair m/f who have shown absolutely no aggression to each other and always swim together. I think the trick is to get them really young at the same time so they grow up together. I also may have just been lucky and have a docile male. I think pearls give you the best chance of having multiple gourami in a single tank without it being a warzone