Mine is clutched for around 10K, and it'll hit the rev limiter at 4K where I live. It works pretty well where I typically ride; some days it'd do better with more weight, but I haven't got around to buying some heavier weights. You might be in the overrev range a little with the 4-6k clutching. If you've got some hills you can pull (next season, obviously), do a long straight pull and see where RPM stabilizes. If it's much over 8300, and definitely if it's pushing 8400, add some weight. Arguably, if you're going to pick a weight and stick with it, you want the one that gets you in the range on the warmest day at the highest elevation you ride (7950-8250; I think I read the most power is closer to the top of that range, but it drops off quick if you overhsoot). You definitely have a lot to gain over the 8-10k setup, but you might not find enough to be worth messing around over the 4-6k setup. That said, there's almost always something to be gained over stock clutching; a lot of it depends on how much you want to squeeze every bit out of it, or if "works ok" is good enough.