It's hard to say; the specs say 90 shots, but that is for an UDMA card: ; The old Extreme IV for example.
Let's assume that the card was 20 MB/s: 90 shots would take 15 seconds. ; So it would have a total transfer of 450MB over those 15 seconds. ; Subtracting the card write, it appears the buffer is about 150MB.
Using a little bit of excel, it looks like you'd be able to get just over 6 seconds of continuous shooting at 6fps before your buffer filled, and then you would be restricted to about 1 shot per second until the card writes, which could take another 21 seconds to finish completely according to my rough calculations. ; Now the more time you wait you'll be able to have larger bursts while still waiting for the original pics to write to the card.