Thankyou for ur reply Drizz, by better files I meant that the increased file size & later model of the CCD of the Mk111 compared to the origional 5D which I'm currently using. I'm sure I read somewhere the bottle neck for write speed was the canon choice of connection from the SD card to processor or something to that effect. The write speed was 133x which meant 20mb per sec , or something similar & folks were complaining regarding slow shooting due to the buffer overload. But if I can shoot short bursts of 2 fps with no buffer problems writing full RAW to both cards I would be fine.Thanks again Pete
First, the sensor type for both cameras is CMOS, not CCD.
Second, increased filesize is not indicative of 'quality', which can be subjective. It is influenced significantly by megapixels, and somewhat by the content of the image which can include the amount of noise and other things which can cause it to not compress as well as a fairly uniform image.
And the bottleneck for writing to the SD card on the 5d3 is the fact that Canon did not use the newer UHS-1 hardware which I personally suspect is partially due to the Digic 5+ only having 1 high speed memory card interface. Although it could simply be that Canon didn't want to put in the necessary hardware interface for UHS-1 since it likely was a bit costlier at the time, and/or they didn't see that the necessary cards would be coming out as soon.
And yes, I suspect you will be fine at ~2 fps shooting, although you likely would eventually hit buffer full. But if you pause for a second here, a second there, you likely will be fine.