I'm an Avon Cobra fan. As soon as these are worn out I'll change to Avon.
I have Dunlop E-4's and they are just fine..No issues at all and intend to run them again when these wear out...Some like the Avon tire a lot and they get good reports...No experience with Metzlers, but many do not like them much....I would recommend the Dunlop if it were my bike...Regards and ride safe
I used to run E3's and have changed back to Stones because they feel more sure-footed on wet pavement.
I change my tires as soon as i see significant wear. Generally around 10K but it varies on the long distance, heavy loads I do. I know others that get more but I hate getting stranded by bad tires. I should add that I used them on my old GW, this F6B and my other bikes.
I run Avon's on the F6B as I did on the Valkyrie. Always had good luck.
Your mileage will vary greatly on these bikes all due to how you ride, type of roads you ride on and also temperatures.
I've run Metzeler 880's and then the 888's on three K1200LT's - 2000, 2002 and 2009 (still riding this one) - for a total of 140,000 miles. Probably 60% of that was 2 up. Never any problem except for whining in the corners (the tires) as they got up in miles. However, on the F6b I liked the OEM Bridgestone's a lot and used them again when it came time to replace them at 12,500 on the rear and 14,000 on the front. There was probably 1,500 - 2,000 more miles left in them to the wear bars, but I never run M/C tires that far down.