E46 Euro Spec M3 is 343HP and 365Nm, 1570kg and perfectly balanced, superb suspension, awesome handling, great rear diff.
The GTA is 1410kg, perfectly unballanced, 250HP and 300Nm, not so great stock suspension, no LSD.
You cannot compare the two in a straight line or on track, unfortunately. I own one 156 GTA, my brother owns a 2004 E46 M3. Even I preffer his car
In all fairness, I cannot say the M3 is an ugly car, it's just not beautiful but it looks very agressive.
PS. Despite what you might think, the M3 engine a huge and very heavy, while the GTA V6 is smaller and lighter
And the CSL is 1385kg, 360HP and 370Nm, need I say more ? It's a freaking beast, inside and out.