Well I have had a carnie hybrid and the first generation was better tempered than any of the local bees I could get. Some of the local ones here are positively vicious - you would need a Kevlar bee suit. What you could do is buy in a queen. Bickerstaffes are quite reasonable and it is easy to do.
With carnies you must always give them plenty of room. Dont wait for them to draw out all the foundation before you stick the supers on. If the brood box looks like its about 3/4 full of bees then you have to give them the extra space.