I did look at extreme pros but maybe got a bit confused as the ones I bought state a transfer speed of up to 120mb/s whereas the cheaper extreme pros, but still more expensive than the ones I bought, quote much lower speeds. The pros I saw quoting similar or faster transfer speeds were £20 or more more expensive. Maybe the pros have faster write speeds and that makes a difference, but I didn't do any research or try and understand and I just went with buying identical cards to the one I already had which proved significantly faster than my old class 4 cards in use.
Faster cards are no doubt available but the ones I've bought do pretty much transformed the cameras I have so I can imagine how much of an improvement even better cards might be but in defence of my choice... they're cheap

I didn't have to think about it and they're good enough for me as I'm very mostly just a single shooter. I may take several pictures quite quickly, but almost never or continuous.