This topic has been discussed several times and yes, there is capacity to be gained by speeding up the beater. As bent said it depends on the crop. In corn walker loss is not an issue so in that case it doesn't help. But in cereals and many other crops it's a benefit. The first and obvious one is cutting down walker loss by doing more active threshing at the beater. In stock configuration the beater turns at a 1 to 1 ratio of the cylinder but because of the beater's much small diameter the tip speed is much less than the rasp bars. You can do a Deere speed up kit (BH78623) which gives you 30% more rpm or a PF Parts 60% kit which gives you almost an exact match in speed between cylinder and beater. This will also give the most threshing benefit and capability to handle more material. Here in Manitoba heavy straw can plug a stock beater but when sped up there is far less chance of this happening.
The down side to speeding up the stock beater is that it's a piece of junk. It can vibrate from dust or just being out of balance. It's not balanced from factory, just stamped steel bolted together. Also the bolts tend to loosen over time and just fall out. Then your only solution is an aftermarket fully enclosed and balanced beater like a PF, Sunnybrook, or Kuchar. These beaters also have more aggressive designs which allows even more material handling capability. Between a good beater and a 60% speed-up, you can expect double the crop flow.