Hi triple4,
Based on all of the information that you've provided, there are 4 likely issues that impacted your performance on this 2nd attempt (and while there certainly could be other issues, there's not enough information here to define what they might be yet).
1) Long 'travel' days can have varying impacts on people. If the nearest GMAT Testing Facility to you is 5 hours away, then there's no way for you to avoid having to make that trip. I know from my own experiences that 5 hours of driving or 5 hours of plane travel often 'wears me out' a bit - and sometimes I need a day to fully 'recover' from that type of travel. Having to take an intense, 4-hour Exam within 24 hours of that type of trip likely means that you weren't necessarily at your best on Test Day. It is interesting that on your first attempt, you would have had 21 hours of 'recovery time', whereas on your second attempt you had roughly HALF that recovery time.
2) Sleeping in a 'strange' bed (and/or staying in unfamiliar surroundings) can also 'throw off' a person's personal patterns (sleep, attitude, overall physical/mental well-being, etc.). Again, the degree to which you may have been affected by this is open to interpretation, but I would suspect that you would probably perform better after sleeping in your own bed - so sleeping in a hotel bed that you're not 'used to' likely hurt your performance on both attempts to varying degrees.
3) Your Quant Scaled Scores on these 2 Exams (Q43 and Q38) are both in the 'range' of scores that a typical 'math thinker' would earn. However, the Quant section of the GMAT is NOT a 'math test' - it's a 'critical thinking test' that requires lots of little calculations as you work through it. To score at a much higher level in this section, you need to become more of a 'strategist' and less of a 'mathematician.'
4) It doesn't sound as if you took full 'advantage' of your two 8-minute breaks. While 8 minutes is not a lot of time, those 2 breaks provide you with an opportunity to refuel (with a snack and a drink) and do some physical activity (running sprints, jumping jacks, etc.) to get the blood 'moving' so that you're pumped-up for the next section you'll face. Drinking water and doing some light stretching sounds like fairly low-level activity. While you probably can't do much about having to travel 5 hours, you CAN do something about how you choose to handle your 2 breaks.
With a bit more analysis on your part, you might be able to deduce other factors that led to that higher score on your 1st attempt. A 670 score is not something that most Test Takers can 'luck' their way into, so I have to believe that you have the skills to score at that level again. With some additional focused study, you could even score higher, but you also have to think about all of these other factors too - so that you can plan out the full Test Day "event" (including the inevitable travel) and minimize the negative impacts that clearly hurt you on this second attempt.
GMAT assassins aren't born, they're made,
Rich