I think I'm stuck with my CM spec I'd really like to up my dps, as you can see i have a lot of EHP and too much IAS the problem is that if I switch my chantodo's will for one with crit dmg or a gem i loose the 3.00001 breakpoint.
Will I go to the lower breakpoint (2.72728) and remplace some pieces with IAS by crit dmg and more crit ?
The choice of breakpoint to use is mostly a personal opinion that depends slightly on what you spend most of your time doing. If you run Ubers a lot, then keeping above 3.0 APS is a decent idea. The same is true if you run mostly in groups. For solo play lower breakpoints are perfectly fine, but you reduce survivability and freeze ability as you lower the APS. In return it makes it easier to raise your dps thanks to using CD over IAS on various slots (weapon, amulet, gloves).
So ultimately it's up to you if you are ok with lower APS. I run at 2.5 and have gotten used to it so I like it but there's some on the official forums who swear by 2.73 or 3.0 and refuse to use lower breakpoints. I'd say be patient with your purchase and if you don't like the lower breakpoint with an OS or CD wand, then sell it back. If you're really patient and get a good deal on the weapon you can get all your money back or maybe even make a little in the process.