Help me understand compliance!

@intactaudio , I can't be sure what you mean. What to you is an insanely high mass arm (in effective mass please)?  and what is a really high compliance cartridge? It sounds fine to you but, I would like to know what is happening where it does not sound, below 8 Hz. If the tonearm is massive enough some very unhappy things are going to manifest and no cartridge I know of (excluding the Decca) has enough damping to deal with it. Hook your phone stage up to an oscilloscope. 
As I said before, I do not use formula or rely on theory. I measure. Unless you measure one has no idea what is going on. "Sounds good" is a hopelessly inaccurate way of describing the situation where the needle hits the groove. T

This is for certain. If you add mass the resonance frequency is going to drop. If you remove mass the resonance frequency is going up. If you can't see or hear the resonance point with a good test record it is because the system is dampening it out. In which case it is not a problem. If you want to increase your resolution hook up an oscilloscope to your phono stage (assuming it goes down that low) and you will probably see it along with some other scary looking stuff.

@yeti42, good for you. Measuring is the only way to go. There is enough variability in cartridges and tonearms that the predicted resonance frequency can be a good deal different than the measured one as you noticed. You are not seeing the vertical resonance because it is being well dampened. 8 Hz is perfect, what I shoot for. You can see the vertical resonance if you use a more sensitive measurement device like an oscilloscope. You can put a seismometer app on your phone and place it on your speaker or subwoofer and you might be able to see it. I have not tried it yet but I will once I get my system set up again. 

Actually bill, non compliance manifests itself as feedback, poor tracking and the stylus hopping right out of the groove.

Skip, lewm and chakster have it right. Chakster's suggestion about the HI FI News Analog Test LP is very important. You have a light medium arm.
It will match up well with the more compliant moving magnet cartridges like anything from Audio Technica, Clear Audio or Goldring. The Goldring 1042 is a favorite of mine. 

Compliance is a measure of the stiffness of the cantilever's suspension. It is analogous to an automotive suspension. Lets use a pickup truck as an example. Empty pickups (no load) have a choppy ride but if you load one up with a ton of brick the truck now wallows and bounces at a low frequency. That is it's resonance frequency. Add weight the resonance frequency drops, take off weight and the resonance frequency rises. The test record will tell you where your resonance frequency is. If it is too high you add a little weight to the head shell. If the cartridge is too heavy or the compliance to high the resonance frequency will be too low and you would have to remove weight (mass) which can be hard to do. So, it is better to start with a cartridge that might be on the stiff side as you can always add weight. But, any of the above moving magnet cartridges will be just fine. If you tell me how much you want to spend and I'll tell you which models to look at.