Having owned both an E34 540i 6-speed and my current 5-speed E46 330i, I can report that the 330 is a hair faster than the 540, though it's very close. Assuming your 540A is stock, a 330 would probably walk it in a straight drag race. Hopefully that gives you some frame of reference.
the '03 M3 will fit your '01 330Ci but, your car does not have the auto leveling feature which could pose a problem. Also the '02+ xenon headlamps are BiXenon, I don't believe the pre-'02 coupes had bixenons. With the '01 sedan headlamps you would have to swap the outer lens out for the coupe headlamp lens. Mr.Motorwerk.
Section 541-1: "CONVERTIBLE BATTERY -. BMW has designed a special Convertible battery tray with link rods which serve to dampen body flexing and vibration. CAUTION: The E46 Convertible requires a special battery which is designed for constant vibration. A battery not designed for this will fail much earlier." 2002 330Ci 6-speed conversion. Hey guys, I bought a 3.30Ci 3 months ago. And it was converted from auto transmission. Now I have 3.38 final drive ratio and it makes my top speed about 230-240 km/h at 7000rpm. Besides, at my normal cruising speeds (90-100 km/h) my engine rev is so high (about 3000rpm @100km/h).