Well linear power can be deceptive, and on the street is generally faster.
Remember 200rwkw on a R32 will feel faster than 200rwkw in a R33, weight, peaky setup etc. So totally agree there. It would potentially be faster too all things being equal.
However @ the power range you are talking about. RB25/260-280rwkw, pit it against a RB20/260-280rwkw - in the same car. It'll be difference like night and day
You'd be talking 500-1000rpm of difference depending on turbo choices, on/off throttle performance would be huge as will the power delivery.
You get more area to the right of the dyno graph, and thats what really is more important on the street. Less peaky setup = less wheel turning and more forward action.
Don't get me wrong - I've had an RB20 before, but it's tough to justify spending 1500+ on exhaust manifolds, plenums etc. You'll never see that value against performance as it's capacity & the head holding things back.