Is it considered a great achievement if I can seduce a nun and would she think likewise....?

First of all, it wouldn't be "" if she consents, in which this case is being explained here. Given the chances that Nuns are NOT to be seduced, it all depends on what his goals were . If he considered it the best thing in the world to do, then it is his greatest achievement. So yes, it is considered a "great" achievement if you consider it to be so.