I would probably say the MSI too
Would these oc'd cards be able to be oc'd even further, or is it not worth the extra money ?
No not really, if it's already overclocked then that means they are already pushing past what it's rated for so that means you'd get a lower overclock than getting a card that's stock but has good cooling on it like the eVGA.
I don't know if they put on another heatsink for the OC'd ones, but eVGA puts on the same heatsink for all their cards which means you get a heatsink meant for the Ultra on something less powerful which makes it easy to overclock.
Not really worth to get the OC'd ones. You'd be better off just trying to OC it yourself with an aftermarket graphics card cooler and heatsink