Delvorin
Grandmaster
I bought mine for 5 million and that's because people slept on it. I think 6 is probably a fair rate for them and, yeah, you aren't going to see many Double Strikes hitting for 300. Tread is a 100% chance to hit and it hits like a truck. Would love a Double Strike myself but Tread is doing just fine.
I agree here. The guaranteed 300 is amazing. I would say that it really depends on the situation if you want to consider which is better. Something like Archdemon, tread is much better as there is no slayer and when you tread and aggro, he doesn't do much damage. Also, when farming, tread is much better as well. I think if fighting much harder hitting things in groups like champ boss or ancient wyrm paras or something like that, double strike is better just because once you aggro, you're pretty much dead unless it doesn't one shot you and you can run. Even then, you have to stop damaging. That's just my take on it.
Sorry to detract this even more. But just saying tread is awesome and worth the gold.