I have a M1000e populated with 16 M600 blades (dual L5430 Xeons with 2 SAS disks). According to the power calculator at http://dell.com/calc/, this configuration has a peak draw of 2850 W -- the peak observed draw to date is 2250 W or so according to the management console.
Having read the available documentation on power distribution, it's a bit unclear as to how many power supplies are required to drive this system if I wish to have full grid redundancy. Obviously I can install six supplies, but I have then provisioned far more power than I actually need. From a pure power input perspective, the chassis should function just fine with only 4 installed supplies (even losing two leaves me with almost twice as much power as I need).
Will the chassis management system will let me get away with this?
Power is a difficult one to give you an estimate on as it's very dependent on the configuration, application etc. That's why Dell provides a peak but we'd agree you'll usually be way under that.
Dynamic Power Supply Engagement (a check mark in the Chassis Management Controller) will do what you're looking to do automatically. You can run on 4 power supplies without any problems but I'd just use Dynamic power to do this for you.