I have the same tires- mso 120tpi 40mm and yeah, they are slower feeling than my 25mm road tires. And they for sure will feel slower than your conti GP tires since those are low resistance.
But i never feel like the MSO tires are slow for what they are made to do. Compared to other 38-42mm tires i have owned and ridden, the MSO tires are downright fast feeling.
Its all just perspective.
If you cant stand how slow they are, toss those 28mm Conti GPs on your bike to ride gravel and see how that goes.
While MSO tires are slower on paved, GPs will be downright horrific on gravel(at least whats around me). Its apples and oranges as the MSO isnt made to excel on paved rides.