Run, don't walk, and go buy yerself some Sportecs. I have a '96 GPz 1100, and the difference that those tires made compares favorably with a new motorcycle. I kid you not. Absolutely amazing. I haven't had them long enough, but they come highly recommended via the GPz mailing list. In fact, I've kept (informally) track of the tire recommendations and tire reports, and (names withheld), here are the top entries and comments, where there appears to be consensus on comments:
D220's wear /very/ rapidly, for no appreciable gain over the 205 or 207 (can't recall which it replaces).
D205's are well-received, if they can be found.
D207's slightly less so, but still well received.
Many are not happy with the BT010's or '20's. The 010's wear very rapidly (median is about 4k miles), the 020's ony slightly longer (5k miles).
The Macadam 100X's wear much better than the 010's *8-10K miles), with approximately the same grip.
The Continental ContiForce gets good reviews, esp. for stickiness, but doesn't last as long. As sticky as the '010s, but less expensive and about the same wear.
Despite Metzeler and Pirelli being of the "same" company, the Diablo and the Sportec *are* different tires. Nobody has run them yet, but they are supposed to be the Sportec + better wet and dry grip, *and* better wear. I'm optimistically sceptical.
The Pilot Sport hasn't been tried by many, but the reports have all been positive. Comparable to the Macadams, D207 and D205, Sportec, etc.. Yes, that covers quite a range, but they are sticky and wear well.
100% (seriously, 100%) of the respondants felt the D220's wore too quickly.
Macadams and MEZ4's, D207, D205, Pilot Sport, and Sportec M1 all rate about the same (well).
I put on the Sportec M1's and am very happy (first Metzeler tire I'm happy with, that's saying alot). "Next" tire for me will probably be the Diablo or the a Michelin. Maybe a Continental, cuz they're cheap and if their price/performance ratio works out, well, what the hell. I'd rather have more sticky than not enough, right?
Oh. And for touring bikes, the Avon Venom X is fantastic.