Brian,
I had a 150 Sigma, and am now chuffed to have a 2.3 Cosworth Duratec CSR under my right foot.
There is no comparison as you would expect and I agree with Paul
I found with my 150, that it felt underpowered and I would struggle to keep up on blats. I had mine RR'ed at Northampton Motorsport after many map changes by CCM.
The Curve was fairly smooth for both torque and power, but what I didn't realise is that the 125 and the 150 Sigma have the same torque figure, and that at 4000 rpm you are making about 75 bhp and at 5000 rpm only 100 bhp
As I used to changeup at anywhere between 3500 and 4000 rpm, it became obvious why it never seemed to be that quick, as I was only using it at about half power.
With the Sigma you really have to keep the revs up to get anything from it
I have the curve I can email to you if you want.
The 2.3 is lazy power, it is there when you want it, but you can drive it potter about at under 4000 rpm and you still have 175-200 bhp to play with. Plenty for me 😬
Rik