I found out that Scyther has 105 base speed and Scizor 65, So would I be able to max EV, beneficial nature evolve a Scyther into Scizor and keep it's 172 speed? or would it go down to meet Scizor expectations? Please help I am going to make a new team and it will have one if they can become super fast!

the speed's gonna drop. I never trained a scizor myself, but I noticed something similar with the flygon family: Trapinch has a base attack of 100. mine reached 98 before evolving. Turns out vibrava has 70 in attack, so my attack dropped to 78(had some evs though) hope that clears it up