Owning both the '05 SEEG (which is probably the precursor to the SG) and the '09 SERG, here are my observations;
The wind is much cleaner / quieter with the batwing to me (6'4" 34"inseam), I had to add a bit (flaps, lowers, windshield and 'am going to change out the dog dish to the GADS) to the '09 SERG to get the buffeting to a tolerable level and to hear the radio above 40mph, whereas the '05 is stock (except for the midsize HD shield to replace the original SG toenail) and I haven't felt the need to change it (could always hear the radio to 75 or so).
The stability in normal riding conditions, (even though the '09 has the new frame / tires) on both bikes are about equal to me, as I can set the cruise at about 85 and pass an 18 wheeler with no hands just about close enough to reach out and touch it with my right hand with 0 drama. The '05 (with the stock lowered suspension from the factory) has the edge, as I had to upgrade to the Premium (spring) shocks and cartridge forks on the '09 to get similar results. The only place where the '09 SERG might have the edge is at 10/10ths in high speed sweepers on rough road, and that might be due to the new frame / tires? As far as crosswinds go, both bikes are as stable as one could expect, with a slight edge going to the SERG.
Both bikes have the same, relatively heavy, feel at low speeds, I feel this is due more to suspension tuning than fairing type, as I have ridden other batwings and sharks that feel much lighter at low speeds than either of my bikes.
I like both bikes, and am fortunate to have both, but in spite of all the hoopla about the Road Glides, if you were to "hold my toes to the fire", I would lean toward the batwing...