Not necessarily no.
You have to log the car.
Just because you have a De-Cat doesn't mean you can lean out the fuel. Doing so may mean you get higher timing pull.
If you lean out the Fuel the car gets hotter, think more oxygen means bigger bang which in turn means more heat. This could mean that your car runs fine on B9 T7 F6 (i can do the same) however if you lean out the fuel to 7 you start to get dangerous timing pull levels. I have some logs going from 976 to 977. When on 976 i would get timing pull of around -3.8 on all cylinders. When i leaned it out to 7 i then got timing pull of -6.4 across 3 cylinders and 7.2 on the other.
You may find that you could run 877. BUT you need to log the car.
I really can't see what the obsession is of increasing the BTF. The difference in power is neglible. I have logs of my car on 877 and then on 976. I gained 2bhp and 5lb/ft so i didnt see the point of running the settings so high. I have done hundreds of logs on my car (317 last time i counted) and found that on 857 my car runs smooth and has no timing pull. On those settings i am only 3 bhp and 7lb/ft less than on 976. Something you are never going to notice on the road. So unless you really are chasing no.s then i would say if you car is running fine on 976 then leave it.
As the chinese say - "Dont fix something that's not broken"
Hopefully that helps