(this launched a whole new discussion thread, thanks! ) http://us.battle.net/d3/en/forum/topic/8197743131?page=1
There are actually sever things to consider (as you would have imagined!).
freeze strength (related to CM procs)
LoH (related to attack speed. i.e. breakpoint)
damage multiplier (a mystical, magical force (sometimes))
I have some threads linked below, but will summarize the data here:
"Equivalent Setups" for Freezing:47.5CC/2.73AS: 69.5% freeze (7.6 CM procs/sec), 6634 LoH/sec, and 6.8x damage multiplier
-and-54CC/2.5001AS/l 70.6 freeze (7.43 CM procs/sec), 5668 LoH/sec, and 7.1 damage
I used the calculator below to generate the numbers...and all generally agree with real-life testing as people mention them on the forums. Generally, you can use an extra ~8CC to strengthen the freeze when you drop to a lower breakpoint. You also enjoy an increased damage multiplier (about 5% more. Of course, some people claim 15% more. A thread today claimed 0%. It's freaky. Generally people think that it has to do with latency. I don't know). The one large advantage that the higher breakpoint has is better LoH returns, almost 20% better (and there's nothing that extra CC does for this).
Why doesn't everyone drop to 2.5001 breakpoint if this is the case?
* First is survivability based on LoH returns as I said before - being able to stand through the worst affixes is a huge advantage....you're not breaking your lock or interrupting your full windup (which is your max DPS). This really shouldn't be understated. Some people move to 3.01 just for this reason....they get over 40% more LoH returns versus 2.5....and can drop some armor/all res simply because of this.
* The other is simply gearing options and cost. If you max out CC on all of your armor pieces (and use nat's set) that gives you max 60CC (and 66 with a CC Nats (unrealistic)). That's impossible. Back off 1CC from each item and that puts you at 54...still, very difficult (but where I am finally at) while maintaining DPS and mitigation. Most people while starting out, and even after gearing awhile, have trouble cracking 50CC. Would stacking CC be easier than stacking IAS? Perhaps. Yeah, probably. But that always get me back to the first point. But: "Pie, just add a third source of LoH!" OK, fine - you'd have to add an extra 200 LoH. Not the end of the world, but now that's taking up a roll on a ring or amulet, just like CC or IAS would. That's not cheap either.
Steve's Simulator: http://d3cmww.com/ ; http://us.battle.net/d3/en/forum/topic/7709121181?page=1
2.5/2.73 Thread: http://us.battle.net/d3/en/forum/topic/7811651308?page=3#45