A few days ago I put a new water cooler in my old dev box, an i7 5820k that is close to 5 years old. The temperatures were barely even better than the old water cooler but it ran OK so I left it there. The last 2 days here have hit 40c yet the core temperatures have barely been above ambient and with a day temperature of 40c, the core temperatures have been about 42c so the cooler is actually working well.
It was a genuine pig to put together and install, a thicker radiator with push/pull fans either side but it meant that I could keep using the old can even though it does not have the top mounted fan holes that the later cans have. The cooler is a Corsair h80i v2 that cost about $150.00 AUD which is a bit expensive but it should last at least some years in what is already a nearly 5 year old box.