1.7GHz from an Athlon XP 1800+ is a decent over clock, The JIHUB stepping 1800+ Athlons are capable of 2.3GHz stable.

Just because it has the same model number or even the same core that doesn't mean it's the same processor, if your looking to over clock you do your research before hand and buy one you know has been clocked up to very high clock speeds. it's as simple as that, or you can get lucky