I am a huge fun of Shelter 901, love the cartridge, even I do not use it now but I would have no problems to continue use it. I do not about those new SME arms: SME 309, SME 4/5/6. I had once, sort time, SME V and I really did not “get” it. The tonearms preferences are a tricky thing and the things not always so clear. I do not think that it was the SME V flat but the SME V was sitting right next to the SME 3012 and that made the SME V in disadvantage.
The resonance frequency – it would be strange for many folks but I do not particularly care about it. The rule of relation between the effective mass of arm + cartridge to compliance of the needle are fine but in practice I observed that they are not always have a direct sonic impact. For instance: the higher or lower resonance frequency might affect excitement of your lower end reproduction. If you play better and heavier TT, do not play warped records and use DSET calcification in class A (the LF in-rash handled just by LF amps and not being intermediated into MF and HF) then you will less care about resonance frequency.
Still with Shelter 901 I preferred heavy load on my 3012. I think the default 3012 and SME 309 has the same effective mass – somewhere around 12g-13g. I do not remember the exact number but I loaded the 3012’s shell with extra mass, somewhere around 20-26g. Search the site, I even posted a picture of the shell loaded with silicone. I think you might try to add some extra mass to the cartridge and to see how SME 309 would response with sound. The Shelter 901 has phenomenal bass. With light arm this bass might be too “straightforward”. Forget about the resonance frequency, your task is (at least my was) to make the Shelter bass more “complex”, very lash and in a way a bit slower then it is. I loaded 901 a bit harder (to 33K) and I played it with much heavier arm then a common sense would suggest. I do not know how useful would it be with your TT, your arm and your listening preferences.
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche