So my 6 month old 4890 died recently, so I sent it back, and have just been emailed saying I've had a new 5830 dispatched. Having looked at specs and benchmarks, it seems like the 5830 is slightly slower? 
So, anyone with experience of the 2 cards, how do they compare? Am I going to have a battle on my hands to try and get something to match?
Many thanks!

So, anyone with experience of the 2 cards, how do they compare? Am I going to have a battle on my hands to try and get something to match?
Many thanks!