I don't know the Vectra M2 variant specifically, but the 4/50 suggests the stock CPU was a 486DX2/50. So an OverDrive DX2/50 isn't going to change much, but the DX2/66 is an upgrade. Depending on the voltage the board delivers and if it can be changed, it may even support a DX4/100.
Just the local Commodore hobo and middle-aged PC hoarder.
eisa on Trademe. A lasting reminder of a Compaq fetish when I was younger.