First of all thanks to steve and wrightwing for your feedback.
Of particular interest is wrightwing's link (which again, I thank) and from where I'll quote the following paragraph:
The JSM is based on Naval Strike Missile (NSM) and was developed in partnership with Raytheon. The JSM has a top range of roughly 350 miles and a low altitude penetration range of about half that. It carries a 500lb warhead and is guided by a navigation suite that includes GPS, INS, and terrain mapping—the latter of which will help out greatly in GPS denied environments.
Ok, from what I read above, the JSM has the chance to by flown towards the target in either a high-altitude or low-altitude profiles. In high-altitude profiles it even have longer range (by 50 nautical miles) compared to the Extended-Range JSOW and on top of that it has the possibility to fly in a low-altitude which of course has a much shorter range but with other tactical advantages.
Apparently it also has more guidance modes (GPS for example).
The warhead is still much smaller but the other advantages may offset this in some/many cases.
“Active stealth” is what the ignorant nay sayers call ECM and pretend like it’s new.