if your certain the car is getting through oil then your best off changing it every few thousands miles
if you think that your going to run out of oil by then you should be seeing it and smelling it coming out ya exhaust
i dont use the dipstick and i know my car aint burning oil
did 6k last time i did an oil change and she had the good part of 4 litres coming out
my advice is dont use the dipstick if u aint burning it off
when changing oil only put 4.75 litres in and make sure it is drained before adding new oil
also unplug coil pack and turn her over for a good 10 seconds before you start her up after oil change
i personally beleive the rattle u get on cold start is the chain bouncing up and down off the cam cover and it is a sticking tensioner