Edit: I think you might want to decrease the biceps and armhole a little more than 0.5". However, that depends on what type of fit you're trying to obtain.
I agree. I placed the oder, and I ended up decreasing the bicep by 1" (if I pinch and measure the fabric, even while flexing, or in any position, there's always over 2.3" extra fabric folded in half (so almost 5" extra overall); so I figured taking 1" off would give it a much more fitted look while leaving a little bit of room for flexibility).
Pinching the seam at the arm hole has much less give. Some of the pictures really exaggerate it (which I believe is partly because of the extra yoke/back fabric). That said, I reasoned that no matter how awkward the position, I could remove about 0.5" there without really straining it much, if at all (largest strain would be achieved if, for whatever reason, my shoulder was pushed forward, elbow out and bent, fist up - like an exaggerated uppercut). If These seem to have yet more room there to remove safely and comfortably, then on future shirts I'll take that into consideration.
The order's been placed. Thank you for everything; it's truly appreciated.