All 3 engines will get you to your power goals. I was really looking for a dollar figure, but based on your power goals you would be barely tapping the RB26 at that level. Its expensive and sounds like overkill for your goals. RB25 sounds more in line if you want an RB series. If you want to check out a well thought out example of an RB25 install check out Rob Fuller's car here: http://www.zcargarage.com/gallery.htm and select ZCG RB 240z on the gallery. His SR20DET swap for his 510 is in the gallery too listed under Other. Just select ZCG 510 Turbo.
Honestly, for your goals the SR20 sounds like the best package. I know you listed no AC or heater, but if you want those items or better yet want the option later your best route is SR20DET. I am not saying its impossible to have AC with the RB motor just letting you know the setup doesn't lend much in the way of space for it.
I know you ruled out the L28ET, but with your power goals its a good bang for the buck. Also, the 7MGTE is a great option for your power goals. Just look at the numbers Clifton is putting up. I believe he said about 350-375rwhp could be achieved on the factory ecu and computor too. Not all of us have unlimited funds on this board so I wanted to point out a few other options you may not have considered.
Have you also thought about brakes, suspension and chassis stiffening, etc. to make this package all work properly? There is a lot more to this swap then just the motor swap.
Good Luck!