Now you're on the right track. Yeah give it more, keep going until you get a light surge at cruise or pinging going up a hill then back it off a couple degrees. Don't worry you won't blow it up if it pings a tad under light load. I'd be surprised if it doesn't end up with 45+ degrees advance at cruise.
Also I don't remember what you said initial timing was but if it's below about 14 then give it some more at idle, that'll also help keep it cool when sitting at lights or in traffic.