Both will be overstocked in a little while, doesn't seem like it while growing up but have a look at full size measurements for the fish you have, some will be pretty/very big (GT, parrot, Sev, Pleco). Life span on the American ones is long too, potentially still have some of your same fish in 10-15 years time if cared for well. I wouldn't get anything more and just juggle the ones you have, it'll pay off more for you down the track. You are probably wanting it to be more interesting right now but it will feel better when you can say I've had that one for X number of years and this one for X number of years, really get to know the individual fish and none are stunted or sick.
On current set-up I'd put all Americans, plus jewels and the pleco in the 75 and look at options on which ones will be moved as they grow. Would put zebra in small tank with SAE, CC and clown pleco and also look at what you're going to do. Both tanks will be overstocked but if they are the current fish and current tanks and you need to put them somewhere that would be my best bet if they were mine.
You need to look at what you want the tanks to be in 6-12 months time from now (and years to come) though and work promptly toward that, you wont have thriving fish and tanks if you leave all of them together unfortunately. May seem like heaps of room and that's crazy but it's best to go on adult size for all the fish when you stock the tank or else it ends up expensive loosing fish, you get more health problems that cost money/are a hassle and ugly to deal with and you never end up with a truly awesome example of any one fish (as a potentially excellent fish can end up stunted and sickly).
Help World Cichlids with its quest for world domination! 
