You would only notice the difference in benchmarks.
I don't know what system you have but if you look here:
http://www.bit-tech.net/hardware/memory/2011/01/11/the-best-memory-for-sandy-bridge/1
there's hardly any difference between 1600MHz CL8 and 1866MHz CL9.
What's the difference in price between them?
If the 1866MHz is more expensive then I'd say it's a waste of money.
If it's a smililar price then it's six of one and half a dozen of the other.
At current prices, and if it was my money, I'd spend £71.99 on these for what difference it makes:
http://www.overclockers.co.uk/showproduct.php?prodid=MY-060-GS&groupid=701&catid=8&subcat=1517
But if it's a choice between the two you listed then these:
http://www.overclockers.co.uk/showproduct.php?prodid=MY-062-GS&groupid=701&catid=8&subcat=1517
The Corsair RAM is 33% more money for bugger all extra performance.
Looks like i'll be going for the c8