If you go Cree X series LEDs are rated for 50,000 hours and then at least 75% Brightness...
LED Fixtures vary greatly in life span. Chinese No Name Imports may have their Driver fail between 9 and 24 months. If the Fixture runs hot with dated generic three watt LEDs it is not uncommon for a row of LEDs to go out after 18 months..
If you DIY using BJB Solderless Connectors you can easily swap out a LED or replace the driver if it gives you problems...Our DIK Kits have been running for over 5 years with an occasional Driver or Fan replacement. Its very easy and with the Makers Heatsink looks are pretty good...
A quality fixture like the Sirius XTC or Ecotech Radion should last at least 5 years with the weak link being the fan in a salt air/dust environment. This is the main reason we added a temperature readout with thermal protection...Years later if you fan fails you will know early so you can address the problem before the whole fixture fails...For extended life expectancy, I like to see a fixture running no warmer than 130F with the norm around 100-110F