There is more to it than Ohm'sche resistance. Your 2 x 0.7 or 0.66 limits your current to the coils, so with lower resistance comes higher current and eventually higher coil charge using the same dwell time. So I would agree that from that perspective there should be enough margin to run the 6V/0.66 Ohm coils. Don't forget though, that with heat the resistance decreases and at 3000rpm + your voltage is more about 13V than 12V. So its more like 10A current.
Now as to the coil inductance: the coils discharge upon shortening the primary side to ground and that creates a strong temporary force field which in turn creates a high voltage at the spark plugs and a back EMF. The force is dependent on the inductance and charge of your coil and that could be a limiting factor. That high voltage on the output (8KV+) does create a higher voltage at the primary side as well which has the potential of damaging your ignition module when running an electronic ignition or arcing of points when running a Kettering ignition.
I have tried it with different coils, but never long enough to see any long term problem.
(Disclaimer: due to my mental state I can not be made responsible for any damage resulting from using the provided information)
Some of the above is fact, some is fiction, some is my personal imagination and some is just simple truth. [me]
... i'm not touring around the world, but neither are most of the guys i see running overloaded spam cans ... [bmwblake]
'72 R75/5 The Blues
StephenB screwed with this post 12-04-2012 at 05:37 PM