My question is, Would it make alot of difference to use three Pyrodex pellets instead of two
Ask your shoulder after comparing the two.
Your hunting out to 100yds. max. Two 50gr Pyrodex pellets (100gr). charge is plenty for deer and will not limit you in any way as long as you marry the charge with the projectile that best performs out of your rifle.
Try your load with the different sabots and use the one that performs best.