to answer the question, it is only bad if you use your four wheel drive the front end will be spinning at a different rate than your rear due to the difference in tire size, which is not good considering your transfer case is trying to make your shafts spinn at the same rate of speed, eventually will cause damage to either shaft or case. Second, where did you hear this about the sulphur?

 

CAUTION !! I HAVE HEARD THIS MORE THAN ONCE ,,,

Running off size tires front to rear affects the BIAS logic of the ABS brake
system and will affect braking performance. MAY NOT BE SAFE.

HOUTEX..

 

i would hold on the them there tires, and either wait for another set to come along, or just buy 2 more and then run all way around.
never want to run different sized tires on a 4x4, it will be that one time when you need the 4x4 and you will pit out your t case or some even worse. not to metion the braking is not set up for.

 

Because of the four-wheel ABS I'd hold off on using those 285s until you get a full set.

As for the sulphur.... yes, the US is going to ultra-low sulphur fuel in all states (they already have it in Cali and Europe)