The Surface Pro 2 and Surface Pro 3 both uses the same Core i3/i5/i7 CPUs; the 4th generation Haswell Intel CPUs.
The Surface 3 uses a quad core Cherry Trail generation Intel Atom CPU. These CPUs are less powerful than a dual core Core i3 CPU. The integrated graphics core in Atom CPUs is definitely less powerful than the Intel HD 4400 graphics core in Haswell generation CPUs.
The Surface Pro 2 (and by extension the Surface Pro 3) will have better performance than the Surface 3.