I was wondering if anyone knows if the B21 and B30 are the same power and

I am planning on buying a b21 or the B30 air rifle with-in the next couple of weeks and I was wondering if anyone might know which gun actually has the higher Feet Per second when shooting a 14 to 15 gram pellet?

Also, I was wondering if either of those guns can be modified and fitted with the RWS spring and or cylinder or are the parts totally different?

Also, where could I buy a new B21 or B30 for a pretty good deal?

Thanks Ray