They're actually in the same eye; the eye with the -3.75 SPH is my left (OS) with a CYL of -1.75; my OD measurement is -1.00 SPH and -1.50 CYL, by comparison.Good question.
Oakley uses total power as setting their limit in what can get genuine Oakley lenses. So it sounds like your -3.75 sphere and -1.75 cylinder are from different eyes... Point being you are under -5.50 total power I'm guessing in your worst eye (-3.75 + -1.75).
Let me know what sunglasses you are considering. I'd say the smaller the better... Also if you're sphere is (-) and your cylinder is (-) then you have more options (non Oakley) if your Axis is between 0-30° or 150-180°. This is called "with the rule astigmatism.
I'm at home now, so I don't have the Rx range charts. But I can tell you yes or no on your favorite frames tomorrow. -4.00 is where many frames Max out with "total power"... But non-Oakley Rx should be able to be done in many frames (if about turbine, gauge 8 L, or double edge, as those are large and will give u thick lenses).
As for your next question... I'm trying to see if it's feasible to make these numbers work in Juliets or Pennys It might be dicey, but worth a shot to ask. Thanks for the answer either way, though! It's much appreciated, believe me.