If youe engine is stock - the VTECH should kick in at 5000-5500RPM.
Your car should be Dyno set. Every vehicle is different.
The 5000-5500 is good because if you were to set it down low it would almost be like having a non-vtec motor. If you set it at 6000, and your redline
is 7000 then its not going to realy do anything. Again, almost like having a non-vtec motor.
The first two pics are examples of where VTEC should be set earlier to smooth out the curve - the latter is an example of where VTEC should be set later to smooth the line out. You want the least noticeable transition from the non-VTEC to the VTEC lobes on your cam. That's when you'll make the most power at every point in the rev range.
Too early and your engine stumbles while it tries to get into the efficiency range of your big lobe- Too late and you have a huge jump where you could have had more power a few hundred rpm sooner.
The first graph had the VTEC set later (4400rpm) so that I wouldn't be jumping in and out of VTEC all the time on the highway, the second is the stock S2000 (6000rpm) that Honda sets so that the customer can feel
the VTEC kick in (sells cars because it's cool, but isn't the best for max power), and the third was just set too early because it wasn't a custom tune.
Hopefully that gives you a more visual explanation of why you want to set your VTEC crossover point on a dyno.
Another suggestion is to unplug the IACV (Idle Air Control Valve) and see if the bog persists.
Finally - you may have a clogged cat. Remove the plug for the Throttle body Sensor and check again for the bog.
If no bog under this condition - your cat must be gutted, removed, or replaced.