Jon, I've also got both started and ready to go into the garden, so I don't have much feedback to give. The Sandia's were seedlings from HomeDepot. I started my BigJim's from seed. The NM Chile Institute has released a Heritage BigJim, which is supposed to be a BigJim with improve flavor and production. That's what I started. I didn't realize the bushes could get so big as is Geoff's experience. Guess I'll find out...
I read somewhere that the typical "Hatch" chili is most often the NuMex 6-4. The NM Chili Institute also have release a Heritage version of the 6-4 which again is supposed to be an improved version both in flavor and production. Hopefully these will yield that great fresh-roasted flavor, you get from the street corners of Hatch during chili harvest season.
I also have a couple NuMex Heritage Joe E. Parker's ready to go in the ground. Looking forward to tasting the difference in each of these varieties.
Good Luck your BigJim's and Sandia's...
Mike-