Re: increased torque and speed, this is going to depend on your battery. If you had a HUGE high voltage battery online for instance, and a motor capable of 4KW, your 1000w controller might be acting as a power bottleneck between the battery and the motor. In that case, if you were to replace the 1000w controller with one rated for 2000w, you would see a performance difference for sure!
Installing a 2000w controller does not insure there will be 2000w available to the motor. That would only be the case if you had a battery capable of delivering 2000w to the controller....
If you're concerned about burning up your 1000w controller when conditions require you to start pushing it's capacity - you can check to see how hot it's getting. If you hear something sizzling when you touch it with a spitty finger for instance, you KNOW, you may be pushing the controller beyond it's abilities....
-Al