My apologies for not getting back sooner(haven't been surfing). Grado has a new statement series all of which have an output of 0.5mv. They have same names as the 5mv reference series, i.e. platinum, sonata, etc. except their called statement platinum etc. The price is the same as their 5mv versions. The big difference is far less turns with thicker wire which drops the impedence and resistance significantly creating better sound. Go back to the Grado web site and look at "whats new" and the Statement series of cartridges for more info. The 1.5mv version was made special for VPI because the 5mv version would overload high gain phono sections.
The moving coil phono section should be able to handle the 0.5mv but you should call Classe to make sure. Around 55-60db of gain is what need.(in the phono section,more is even better)
About the other cartridges, I have not heard them and can't comment. Regarding hum, the 5mv version will hum in the Rega as it gets over the motor, towards the inner grooves. The 0.5mv version shouldn't because of it's much lower output. Happy listening.