In general you can figure about a max of 350 degrees for the cylinder head...maybe a bit more around the exhaust ports. I'd say more typical would be in the 300 degree range.
Most "engine enamels" are good, but they will discolor around the exhaust ports. Everything seems to eventually discolor around the exhaust ports.
Duplicolor makes a most excellent high temp "ceramic" paint. I use it on headers, holds up real nice...but doesn't even cure till it gets about 400 degrees.
A good way to test engine component temps is to have a good store of small mammals that you can press against the hot engine part. The length a pitch of their screeching will tell you how hot it is.
and an alternative for you peta types out there, i saw a thing on television the other day. its a thermometer for measuring engine parts that you just shoot a beem at the area and it tell you the temp. it was on one of those car shows on speed. just think of the possibilities.
jb, you go by the squeel huh?? i usually go by how deeply i can brand em.
I used to use the branding method..but I got tired of shaving them first so they make positive contact with the engine part. Course with the branding method you can use them more than once, the squealing method tends to make the little critters a single use tool.