Fit a PR3 front and PR4 rear to the 600, I have that combination and it is very good.
I also found that the PR3 front wear pattern is much better than the PR4, a few I know have noticed the same and have gone the PR3 front PR4 rear combination. Only option on the 600 if you want PRs
The other option is a Metzler Sportec M7, which I have on the 1000 and are an awesome tyre. Good wear, I have 3000 fast miles on them on the 1000 and no squaring off. Great grip and turn in.
If anyone think the M5 are good they should try the M7. Only fault I had with the old M5 was that they wore out to quick. M7 s are wearing much better. I have gone through M5s in 3000 miles whereas the M7 has 3000 fast miles and is almost like new, more side wear than centre.
I found that the wear pattern on the Front Metzler Z8 on the 600 was not great, a bit like the Michelin PR4 on the 1000. Took them off both bikes when they were half worn, no confidence in them at all wet or dry.
Nice thing about the Metzlers including the M7s is they do not stand the bike up if you have to brake mid corner (don''t ask how I know that)
I have not tried the T30 but have heard good reports on them
Flakey Sportec M1s are gone off the market with 10 years, they were a great tyre back then. I track dayed with them in dry and wet, never once let go. Only fault I had with them is they only lasted 2500 miles on the 600
Quite possible you got a set that were well outside there date and had gone hard.