What should I expect moving from MM to MC?

Zarzu, you say MC cartridges are”faster” because they have lower moving mass with the “same suspension “. Yes, MC cartridges tend to have less moving mass compared to MM cartridges, but no, the suspensions are not the same.  MM cartridges tend to have much higher compliance than a typical MC. That high compliance should enable an MM to better navigate the groove undulations. And if low moving mass is your god, then you ought to be using an MI type; MIs have the very lowest moving mass possible. My point is not to defend MM cartridges but to call attention to the fact that the best test for comparing cartridges is a listening test. If you have an open mind, you’ll be pleasantly surprised to find you don’t have to spend $10,000 on a LOMC cartridge  to achieve your own Nirvana. And these empirical arguments audiophiles make without actual supporting data are sometimes hogwash.

“Dangerous, misleading, and wrong-headed”

You got that right.

Many manufacturers publish frequency response data limited to the "audio bandwidth", which is generally taken to be 20 Hz to 20kHz.  However, nearly any good cartridge has an upper end response extending well past 20kHz.  The fact that one manufacturer publishes data out to 25kHz does not at all mean that another cartridge for which the data only show the response out to 20kHz is relatively bandwidth limited.  There are many cartridges (of all 3 types) that have response out to 40kHz or even 50kHz.  That's not a good basis for a priori judgment of "goodness". 

I agree with others who suggested Audio Technica or Soundsmith in lieu of Sumiko.  I have owned two high output Blue Points and found them unexciting compared to any of several very good MM or MI types. Not sure you have enough gain for the OC9 without either a SUT or a new phono stage.  Find out the actual gain of your built-in phono stage, in terms of db.  You'll need to know that if you want to consider mating it to a "high output" MC.  (I don't like high output MCs compared to the best MM, MI, or LOMC types.)

To answer your opening question: "What should I expect moving from MM to MC?" My answer is you would then appreciate the differences between the two particular cartridges; such a comparison of one vs the other would not yield information on which you could generalize between the two genres of cartridge, although some audiophiles do that.