200w is just the wattage the speaker is rated to handle at max.Yes the 50w OTS will be a perfect match. You could drive a 4x12 of EV-12's with the 50w. SRV used the Marshall Major And his Steel String Singer to drive 4x12 Dumble cabs loaded with Ev-M-12L (sometimes 6x10 Marshall bathtub cabs) with EVM's. He would also use Ev15's in his Vibroverbs because the  JBL K140's would blow. Ev's are really the most transparent, efficient, and powerful speaker for guitar (other than some Fane stuff). Chances are the 50w OTS will likely break up before the speaker does.