I can't find the specs on that cam. They aren't listed in your link.
I also don't know the stock specs for that engine. I'm not surprised at all that your timing changes made a noticable difference. I don't see ay reason that engine wouldn't take 38 deg. HAve you tried going over 35?
IF you are looking for mild improvement in camshaft, consider the stock duration +5. or minimum
[email protected]. .025" over stock lift or min .500. LSA stock to -2 deg.
That will not be anything wild, but you'll notice a difference.