Lower end Soundsmith cartridges vs others in same price range?

SoundSmith is MI, go for it, at least you don't have to bother with re-tipping, you can get SoundSmith with user replaceable stylus or Peter will replace it for you for the lowest possible cost as the manufacturer.  

It will never happen with MC if you will not ship them to the manufacturer, the cost will be much higher. 

if you on MI look into Grado low output models or Hana  LOMC from MC.

I'm thinking of upgrading to a 1200G later this year. I'm now thinking the ZEPHYR may be the way to go, especially switching to a higher end TT. May be the last cartridge I would ever need

As you know Peter at SoundSmith likes Grace MM cartridges and you can read about it here, he’s servicing them for others and even produced his own replacement styli for them. It is safe to buy one of these, the best are F14 and LEVEL II models. If you prize his work he could always repair those vintage Grace beauties. I am a big fan of Grace (but i use only original styli with Grace pick-ups).

Some bad info here. Yes Soundsmith is MI, but the replacement is factory not user. Grado is also MI, but different.Also, for low cost, I would advise to use Soundsmith high output and spend less money on the phono preamp. Soundsmith HO is like getting a free SUT without the penalty of increased moving mass as for a HOMC.