V=I*R, so I=V/R

Pi (power in)=I*V

Po (power out) = τ * ω (torque*angular speed)

Torque is calculated by:

τ = (I * V * E *60) / (rpm * 2π) (where E is efficiency)

So you can infer that your current PEAKS will be the same as the constant current were the motor just "on", since PWM is just pulses of 5v and we will say, for ease, that your motor impedance does not change (it does because its a dynamic load but for our purposes here we can say it doesn't)

But your RMS voltage, current and power will all be lower, because any PWM is actually a square wave AC with a bias of 1/2 peak voltage (in other words it stays positive).

So. Your torque will be reduced, as will speed. It can't be any other way. However, if you can get speed to reduce by enough, your torque will increase and balance out.