I can speak to Minnesota's 4+4 schedule (I assume Mayo's is similar):
The 4+4 structure has much less clinic time over the course of residency: 94 days versus 156 days. The schedule works like this: alternating periods of four weeks inpatient (Wards, ICU, Cards) and four weeks consult (electives) months with a single clinic day/week during consult months. So, you end up with 26 days/year of scheduled clinic versus 52 days/year (assuming 5 days of clinic on the +1 week). During intern year, there is a 4 week block of "clinic immersion" where you work 8am-4pm (often less). The down-side to this schedule is a few more inpatient months as a senior resident (but you still have less clinic time, a protected three months for research or electives abroad, and weekends off every other month). I'm happy to field more questions if anyone has them.