I think if you crank them up to 100% duty cycle standard injectors can be good for up to 180rwkw, ive had people tell me they are making over 200rwkw with the stockies but i don't really beleive that.
RB20 det uses top feed high impedance injectors whereas RB26 uses top feed low impedance injectors, so i think you can use them with a resistor pack or something.
rb25 turbo is substantially bigger than rb20 but if i were you id save my money and buy a brand new turbo. I mean ppl sell used rb25's for like $400+ and for around $1400 you can by a brand new, much better turbo, do it once do it right.
but yea, this gets asked all the time and has probably been answered in much better detail in another post so using the search button might be more helpful