Agree with the others. A Shelter would give you the more extended highs you're after while retaining the bass and midrange heft you have now. The stylus profile alone compared to the Grado will do that.
Benz is another possibility in a mid-compliance cartridge.
If you do go with a Shelter or other low compliance cartridge on an RB-250, Twl's HIFI mod is a cheap, easy and utterly mandatory mod. You won't believe your ears. Check it out here:
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1032024188&read&keyw&zztonearm+tweak
Benz is another possibility in a mid-compliance cartridge.
If you do go with a Shelter or other low compliance cartridge on an RB-250, Twl's HIFI mod is a cheap, easy and utterly mandatory mod. You won't believe your ears. Check it out here:
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1032024188&read&keyw&zztonearm+tweak