I have spent time in both areas, they are definitely similar as stated, but I see some differences (I could be easily be proven wrong.) I think I would go with the following as differences:
1. 64 seems more remote to me than 67, but when you are way back in 67 it is definitely remote. Maybe it is just because 67 has a pretty darn good access road through the middle of the unit.
2. I think the goats in 67 are less migratory than 64. I think the goats in 64 will more easily migrate out of the unit (so if you are planning to hunt late, be warned.)
3. I think there are more goats in a smaller area in 67 (higher density), so probably easier to find a high 70s buck there than in 64.
4. I think 64 has a better opportunity for a buck over 80, though it is possible to find a monster in either (upper 80s).
If I were hunting early, I would hunt 64. If late, I would hunt 67. Actually, just give me a tag and I would hunt either anytime!