Seems there are some misconceptions here.
The number of blades make no difference to the CP of the design.
The number of blades makes no difference to the tsr of the design. (can be the same for any number of blades)
There are no efficiency differences between blade numbers at the shaft.
If you go to a blade calculator (say altons) and plug your tsr, blade number and diameter in, the rpm and power at the shaft is the same for all wind speeds with any number of blades..... so thats the theory.
In PRACTICE this is not so easy to achieve. If you do do the above exercise, you will find the blades are impossible to actually build and have any strength when you get to high blade numbers.... they are so thin to achieve the same high TSR we expect with say 3 that supporting the force on them is no longer trivial.
Luckily, some folks (such as here:
http://old.windmission.dk/workshop/bladenumber.html ) have actually built and operated 12 bladed designs, and achieved measured CP in the reigion of 0.47. Thats not too shabby at all.
If you only buy pre-made blades, then the more you add, the lower the TSR and the higher the torque, and all the things mentioned by Chris will come to pass...... but if you design for a TSR and build to those specifications (if possible) then blade number makes no difference.
Commercial mills didn't miss this. Two blades are cheaper to make for the same TSR, but wobble, and have their own problems. Three blades solve all those problems.... even though it is 50% dearer to make.... so they make these. Making three blades to go as fast as the 2 blade design is structurally significant, so they settle for a slower three blade with a bigger gearbox
5 blades for a given TSR offer no more power , no more ....or less speed, no better CP, TSR or any other advantage other than they will cost more to make, and be structurally weaker for the same TSR as a three blade version.
If we want more torque on a practical scale, we add more of the blades we have that are strong and available..... and we find lower speed operation, and higher torque.....but ONLY because we didn't change the cord and the pitch.
What we see and measure can lead us to the wrong conclusions if we dont fully appreciate what is really happening.
The most important factor is MATCHING THE LOAD to your blades, and blade count will make no difference..... loading will.
If you chose 5 blades of a three blade design, you will get more torque at a lower rpm, but you will need a much bigger alternator to match it physically (more magnet and copper and steel) for the lower rpms.
...............oztules