With the same bullets, the 6MM is about 100-150 fps faster than the .243! Either one, with good 100 gr. bulletsmakes an excellent minimum caliber deer gun! The 6MM Rem. started life later than the .243 Winchester, as the .244 Rem. It had a slower twist rate than the .243, and was not as accurate. It was reborn as the 6MM Remington, with the same rifling as the .243, making it as good, or better than the .243! But, its reputation had been sealed, and it never gained the popularity of the Winchester.
So, ammo availability could be a slight factor with the 6MM.
As for Tasco scopes, I'll never own another one! I'd ditch the scope for a better one ASAP!