The party I ended up running for was as follows:
dragonborn paladin 1
doppelganger warlord 3
efl ranger 2
human rogue 4
dragonborn cleric 4
dwarf fighter 4
They faced a Young Green Dragon from the MM, it is a level 5 Solo.
The dragon performed underwhelming. Not only were my die rolls crap during this fight (I missed the double attack every time but once...), but the dragon did not have the damage output to match the PCs of that group above.
The Young Red might still have been too much, but the green was too weak.
All in all running the dragon was fun. Next time I will use one that is a bit tougher... I'm done going easy on them.
The first encounter of the night, 4 Dark Creepers and 1 Shadowhunter Bat was more of a challenge for them.
Everyone did have a great time though, so I'd say it was a success.
Did the dragon have room to fly, hovering plus reach seems like it would be a big boon for the dragon.. Looking at what the dragon can do and with the proper enviroment I know I could give the PC's a run for their money.