The newest SD cards (UHS-II) are well over 200 MB/s read and write (bus speed is 312MB/s). The fastest CF cards (UDMA 7) are limited to 167 MB/s. CFast (serial interface) used in some digital cinema cameras up to 600 MB/s but not compatible with CF.
Let's compare the Sandisk Extreme Pro in CF and SD. This information is right off the B & H Photo site on memory cards.
Sandisk (newest) Extreme Pro in CF Maximum write speed = 150 mbps however.....
Minimum guaranteed sustainable write speed (
guaranteed continuous write speed for video users) =
65 mbps, optimized for 4K users and Full HD users according to Sandisk of this card on B&H Photo site. Great choice for Canon XF200 and XF300 users for recording 50mbps continuous on these cameras in MXF format, and 5D3 users I imagine.
Sandisk Extreme Pro in SD Maximum write speed = 250mbps, however.... (you need UHS II device that is compatiable) and the other thing....
Minimum sustainable write speed of this newest SD Sandisk Ext. Pro card UHSII (continuous write speed for video users)
=
30 mbps which is states in overview page of product, not mentioned on 2nd spec page. If your camera does not record over this rate (such as new highest quality MP4 available format at 28mbps or in AVCHD) you are fine.
CF Extreme Pro looks better on the minimum sustainable continuous write speed and that is why professional film makers if they had the choice in their cameras would like the CF cards. Mind you, some would feed the video out to external recorders to take advantage of even higher data bit rates.
What this only means is that although both these cards are capable of recording at very high speeds both SD and CF, there is possibility of some small blips in signal if it drops below speed (although it will still run at the fast speeds at least some of the time, or maybe majority of the time (who knows?). For prestine clean video the CF extreme pros are preferrable because of
faster minimum continuous write speed 65mbps vs. 30mbps in SD new Extreme Pro UHSII. Or many pros would consider going external recorder for very high data settings for even bigger clean video with less compression.
Both the new Extreme Pro SD UHSII and CF are ready for 4K and Full HD, however newest CF is still faster for video for continuous sustained write speed and thus cleaner signal, for very high video bit rates.
What does this mean to mostly still shooters, SD or CF are both fine, pick your own flavour.
For hobbyists or enthusiasts as video users, and depending on recording format used for Full HD or 4K if available on the camera, new SD or CF would likely be more than fine.
Also in 10 years of use, never bent a pin on a CF with over 100,000+ photos taken at least. Currently 85,000 on my D700 according to the shutter count site, and I bought new in Aug. 2009.