Baph

From the tyres you've highlighted. The Z6s are known to you, so I'll leave that for a second.

BT021's, I haven't personally tried them. However, The Battlax (021's) are the super-cession of the BT020, which only really differ in tread pattern. They also introduce dual compounds for the 021's. They're a sports-touring tyre, just as the Z6's are. I think you'll get around the same distance out of BT021's as you do Z6's, possibly less so, but you'll get more grip. I personally wouldn't change from Z6 to BT021 for longevity alone.

Back to the Z6's, you know what they feel like. The only thing I'll say is that I generally get around 8k to a rear. The secret to tyre longevity is smooth riding. The harder you are on the throttle in particular, the more rubber you leave behind.

The Pilot Road 2's. Well. Fan-blooming-tastic tyres! BUT it depends on your usual routes. The PR2's are dual compound tyres, meaning that the centre is harder than the outer edges. This has the obvious advantage of more grip in the corners and longevity in the straights. Boy do they grip! Wet, dry, doesn't matter. I have pushed the bike harder on PR2s than I have on Z6's. I've also recently gone back to Z6 because of a puncture. I'll be getting PR2s again as soon as my repairs are done to the tyre because I like them so much. I'm not going to wait for the Z6 to wear down.

I'm not sure about the longevity of PR2s, as I haven't had a full set of use yet. I have heard of 1000cc bikes going touring on PR2s and getting approx 6k miles out of them. How that will translate to my bike, usual routes, and my riding, I'm not sure yet.

Another thing for your consideration, is tyre pressures. There is a manufacturers recommended setting, and you can go either way of this. I wouldn't advise you play around much, but going one way will generally improve grip, going the other will improve longevity. Go too far in either direction & it's counter-productive though. For example, the PR2 recommended setting is 33/36. I personally prefer them at 36/42. They're stiffer, and grip better (less carcass movement I think). However, I'm probably sacrificing longevity for the grip. That's always a trade off you have.