A few questions first:
I’m not sure what you mean by “We completed installation of OSB baffles about 6? from the underside of the plywood roof decking”. Did you create a 6” deep ventilation space between the roof decking and the baffle all the way from the soffit to the ridge vent?
What size of material are you using for the roof rafters, is it 2”x10” framing?
Is it OK in your area to install wood paneling / T&G without a fire-resistant backing of drywall?
Check with your local building code / fire officials and insurers for specific information on foam panel board installation requirements / what type of fire blocking surface it requires in your area.
Since you’re in Minnesota I believe the minimum required insulation value for a new construction attic is R-38. However, federal standards recommendation oscillates around R-50 for your climate. To lower the cost and still use closed cell insulation you could spray roof decking underside to get at least 3” thickness (no baffles / directly on OSB).
That should minimize possibility of condensation and give close to R-20 value. You can fill remaining space (assuming it is 2”x10” rafter) with 6 inches of fiberglass batt (or cellulose blown-in) insulation which would give you additional R-20.
You could also lower spray foam thickness to 2” (less isn’t wise because you might end up in condensation buildup on the OSB), staple 6 mill plastic foil to the rafters (not under T&G) and blow-in cellulose insulation into the remaining space.
Additional solid foam boards (even better if they are laminated with reflective aluminum foil for vapor blocking and heat reflection) would give you extra “R’s”. You can use aluminum duct tape on all seams to provide even better air tight envelope. Again, check if they can be installed on the ceiling with no drywall layer on top of them, just T&G
You can replace fiberglass and cellulose with cotton butt insulation which has very good R values as well – http://www.greenbuildingsupply.com/utility/showProduct/?objectID=663
Any combination of insulation that will give you over R-40 value with a good vapor retarder on the warm side will do (you can additionally put a coat of a moisture vapor barrier primer / paint).
Also, without insulating spray foam applied directly to OSB you definitely need those baffles and they should be as wide as the rafter space. During my inspections I’ve seen mold developing on both sides of the baffle if there was any space left between the baffle and the rafter wall.
One thing to remember when applying spray foam to the decking is that roof leaks will be extremely difficult to detect and often result in extensive roof decking damage before you notice any problems.