I pulled up the specs for the Diamondback models you mentioned. For me neither would be a choice as the eye relief (as some have already mentioned) on both is well under what I would put on any .300mag. FWIW, I happen to own four rifles in .300mag in one form or another. With eye relief as low as 3.1" and 3.3" both those scopes are a no-go for me.

I'd suggest a Leupold VX1 or Rifleman in 3-9x40 instead, for just a bit more $$. They have eye reliefs of no less than 3.7" and up to over 4" depending on what power it is set on.