Help with cassette, worn or not? I have done exactly 2879 km on my cassette, and currently I got myself a new chain which is a third for this cassette. With first chain I made 1985km, but I already noticed a significant degradation in shifting so I replaced the chain. Then with the second chain I did only 894km, but did not experienced misshifting, I just measured the chain with a chain tool (two different tools) and and it showed lots of stretch, so I replaced for the 3rd time. Now I am wondering will this chain with this much "worn" cassette last at least some reasonable time/km/miles? I have done 33km with this new chain to see how will it perform and it didn't skipped at all, I could still call it a precise shifting through all the gears, but on some cogs there's a "grinding" feel if you know what I mean. I always keep my chain, cassette and crank clean after every ride, road or off road. So would it be wise to get a new cassette at this point? Or try and see how long will this new chain last? In case someone is interested the cassette is shimano 50-9 11-34, first two chains were hg53 and the 3rd one is kmc x9.
By looking on the shape of the tooth on the biggest cog, it looks worn out and a time for a replacement. Grinding feeling on a clean chain is always a sign of wear.

Also worn-out cassette will will wear out chains much quicker. And you already feel that - second chain got only 50% of usage from the first chain. 

I would just replace the cassette, before the new chain is also stretched out. 

p.s. you are far too precise with your mileage!