Higgspeed GP vs Meek (Denco) pipes dynoed together with stock 71mm h2b cylinders. 
-VM38 carbs
-Cylinders raised 1.5mm
Note: meek=Denco

Below is the Higgspeed GP vs Meek (Denco copy) 

I have dynoed denco vs higgspeed earlier, and have tried them out on different set-ups on street many many times. 

This GP style is significantly stronger in powerband than ordinary Higgs pipe as I see it. 
The pipe body itself is identical as far as I can see. This Power increase must be because of what I mentioned earlier. I suspected a proper baffle cone ending in a stinger is a better solution than the cheaper silencer tube that does not have the baffle cone profile. 

Higgsy GP now gives almost same peak Power as Denco, but at an considerable lower rpm. 
As you know: 

Power Equals to torque x rpm. So, the New Higgs pipe gives a lot more torque than earlier, and also versus the Meek (denco) 

BUT............the added Power in powerband due to the harder pulse given by the baffle cone, also mess up a bit prior to powerband. That is just physics. So, this Higgs pipes is a tiny bit weaker than Denco in the 4000 rpm area. Usally, the regular higgsy pipes is stronger. But I choose the GP, no doubt!!!!!!!!! Much better baffle cone and stinger design. More aggresive pipe. 

Below are both Power curves and torque curves:

These tests are not 100% accurate due to lack of 100% jetting using my air to fuel ratio sensor. But they most certainly gives strong indications. And yes......it is very satisfying pretty much predict the results prior to the tests. 
And I guess the same thing is seen on the gp higgs versus ordinary higgs, where low end is a bit weaker but powerband much stronger, that we saw when I changed the 22mm stinger to a 25mm stinger on my custom Jollymoto: 

It creates a stronger returning wave. GOOD for supercharging, but same increase also mess up scavenging and push down fresh gases in the piston ABDC to piston closing transfer area. 

That is pretty much confirmed now, as it is seen on 2 completely different set-ups with 2 completely different cylinders and pipes. 

But since the cylinders are original, only raised a bit and With a decent size carbs, I believe the test is valid. 

Higgsy pipes are, due to the tuned length, very suitable for ported engines as well. 
TNT or Figaroli pipes are not, as they are very short, and you get too much rpm. 
When too much rpm, it's less time for scavenging.