Canon 5D Mark III is slow in RAW.
I have been shooting using RAW + jpeg for quite some time.
I was able to take only six shots in a burst before it slowed down.
Even with the fastest cards it remained the same.
Due to some discussion initiated by me on NSN, I switched to RAW only.
The difference is amazing: I went from six to eighteen frames continuously.
Still six frames per second of course, but I can now take eighteen frames instead of six or seven.
I was also advised to remove the SDHC card and use UDMA card only.
I'm passing it along in case you need it at all.