Back to the discussion about HP/liter, DI, etc, BMW went "balls out" on the M5's V10 in terms of HP/liter (for a such a large engine), and torque/liter. Although the M3's V8 seems to eclipse the V10 in the HP/liter category many believe that the M5's engine is making more like 520 HP (based upon its stellar performance figures for a >2 ton machine) so they may both be about equal there.
However, the M5's torque curve is FAR from flat. It rises dramatically at around 6000 and thus its peak torque is pretty impressive, esp. compared to the M3's. In achieving this top-end performance BMW sacrificed both low end and mid-range torque(where is makes much less than its old 5 liter V8 in the previous M5) and FUEL ECONOMY.
Although you'd think folks who can afford a $80K+ sedan would not care about the poor fuel economy, I know M5 owners complain about the lack of range when they average 12 MPG (EPA 11/17) in normal driving. With a 16 gallon tank many can't even go 200 miles before needing to fill up.
I think BMW was aware of this and chose to provide the M3 with a more usable torque curve and make it a more fuel efficient powerplant.
We can leave the gas-guzzling, high-end torque curve to the CSL.
Driving sideways: It's not faster, but damn it's more fun!