i think the o-l modified rb250 is a killer arm, but then again, i've not had any of the really spendy arms in my set-up. this is one area, where, if i like the sound, i take the reviewers' word that it's good... :>) as i replaced the ft-3 at the same time i replaced the motor/power-supply, i can't say how much the improvement was attributed to the arm vs. the motor
i highly recommend replacing your linn's stock subchassis - i fabricated a corian subchassis & delrin armboard for my old c&j walker 'table, & it made a *big* difference...
re: cartridges, i obviously hope to have my socks knocked off w/my rebuilt lyra (which the distributor assures me crushes the stock wersion), but, frankly, i think the ortofon (0.3mv) is really nice - it is *much* more neutral & smoother than the blue-point it replaced.
regards, doug