it's a given that you will get different numbers from dyno to dyno... depending on whether or not one is load based (mustang dyno, dyno-dynamics) vs. inertia based (dynojet) but with proper calibration and strapping the number should be very similar...within reason.
i voted R35 because it is a relatively new platform where typical power-adders do not work as planned... depending upon what your whp goals are, you may find yourself struggling and inept...this is one reason why i love the R35...it doesn't give it up easily...
if you can prove yourself with this new technology, then you are on top of your game...