Is 8.7hz too low for tonearm/cart resonance?

8-11hz is optimal, you're fine.

If you know the effective mass of your tonearm, you can go to cartridgedb-dot-com and double check everything with the cartridge resonance evaluator there.

Dear Alun: +++++ " Now I'm faced with this resonance thing. " +++++

which the problem you have?, you don't say about.

+++++ " and the TT is somewhat suseptable to footfalls. " +++++

sorry if I don't understand very well with that statement: do you mean that you are hearing music as you walk in your room near the TT? that's the way you listening?

normaly I hear music at my chair listening position and seated. Who cares if you are seated that the TT is suseptable to footfalls anyway. ?????

Regards and enjoy the music,
Raul.

Try to get some well solid support to TT may help.

Good point Raul, I am usually sitting however I have others in the house that walk around and this can cause "skipping" if walking near the table. I think this is more a matter of support though and not one of resonanace.
I'm in the middle of changing my arm. Moving from an ET2 to the 10.5" Jelco. The Jelco just seems so heavy that I'm a bit concerned thats all. I think I'll pull the trigger anyway. The arm looks really well made and a decent value that I don't think I can go wrong.