What everybody here knows but hasnt really mentioned, is that every mix of large cichlids is a risk. Just because it works for someone else doesnt mean it will work for you. The above post proves this - 7" Red Devil, 8" Jag , no aggression !! Most large CA's can be either killers or pussycats depending on the individual, so whatever you decide you wont know if it'll work till you try it, and even then they could all be peacefull till they get big, or someone matures, etc, then you could have problems. This is part of the 'fun'. Just make sure you can offload them if you have to. But apart from being a neccessary 'plan B', this also makes it easier, because you can try stuff knowing that if it doesnt work its not a big problem.
Personally I would stay away from salvini - all the ones I've had have been professional mouth-wrestlers - unless everything else is much bigger.
Btw, assuming your tank will have about 20" depth of water in it, it will be about 90 gallons(UK), or 110 US. A 72x24x18 is 18 cubic feet, but allowing for thickness of glass (about 10 gallons), a realistic fill level (not right to the top), and a bit of decor, you're looking at about 90 gallons.
I'm in Carlisle. If you can get to Maidenhead Aquatics here they have quite a few CA's - medium argentea, red devils (nice but rarely peaceful), JD's, and 1"-2" young of a few spp.
I've got 5-6" synspila pairing up, so I will shortly have 2 of these going free to a good home if you're interested, also a 5" Thorichthys ellioti (firemouth group but pretty peacefull) and a 6" Geo. altifrons (probably too peaceful).
If you do go for just a pair of festae be careful, because 99% of young sold as festae in UK are urophthalmus - just as beautiful IMO, and a lot less aggressive.
