Close QuickTime player and stop overthinking this or you will make huge mistakes that will be difficult to fix.
Your computer is fast enough to edit all flavors of DVCPRO including DVCPRO HD. Hell, an old G4 could do it.
By the way…you need to figure out what you are editing.
DVCPRO is SD and 25mb/s
DVCPRO 50 is also SD and is 50mb/s
DVCPRO HD is 100mb/s
There is no DVCPRO 50 HD