BMW mechanic here! Driven them all,the conver is v.dissapointing,shakes over bumps and not major fast the coupe is 10 times better.
Even the E46 shakes over a rough road but not quite as bad- its the motor that leaves the impression though!

The 3.0 has a better power delivery and gear change although only a 5spd than the Evo.The 3.0 also has a less stressed engine which hardly ever seems to go wrong in any way.

The Evo has it all on paper though over the 3.0:
Alloy doors,revised suspension caster+ cambor,quicker steering,floating disc brakes,and the rest.

The coupes drive so much better,try both