I've found them very similar from f2 to f8, both have little to no distortion, little to no focus shift, good sharpness, medium contrast, bokeh to die for, and excellent build quality.
The asph cron can have some aperture reflection flare in or towards the sun. The pre-asphs flare is mostly at 1.4 and is the veiling type, or the crescent if shot at night and with light at certain angles.