[Closed] 10 speed cassette life

The chain on my 10 speed Gary Fisher Rumblefish has worn by 0.75% already according to the Park Tools gauge. I've now replaced the chain with a £20 SLX version.
The question is, how can I best extend the life of the £50+ cassette?
1. Keep replacing the chain at 0.75. Will the cassette last forever?
2. Replace chains twice at 0.75 and then run the third to 1.0 and put the 1st and 2nd back on running them to 1.0 as well? Then replace the cassette and chain.
Any other suggestions? Going back to 9 speed is tempting!