How much does your team weigh? Do you spin or stomp? What is your terrain? Do you shift underload? Do you cross-chain regularly?
If you are a sub-275 lb team, who rides on flat terrain, properly shifts (ease up when shifting / avoid cross-chaining), spins and maintains the chain, then 6k is low.
If you are a plus-400 lb team, you shift under full load regularly, cross-chain, you stomp while riding, are in a wet, mountainous environment and don't maintain the chain, then 6k is not be too bad.
My tandem has several of the 2nd issues (big team, mountainous environment - small chainring gets used for >10% of every ride & my stoker likes 75 rpm better than 95) so my chainlife isn't what it should be.