you should get the 4:1 ratio but i dont believe in rrfpr's. Try the SDS EIC Additional 2 injector kit if your looking to upgrade your intercooler pipes and intercooler aaron garney will hook you up with a decent price but with the sds unit you would have enough fuel for 400rwhp on a 5m considering you have all the internals forged and up to the challenge
go to www.sdsefi.com for more info. tihink 034efi.com has a similar product, but it probably hasnt been used by as many people.
basically the advantage here is you keep stock-ish sized injectors so at idle, off-boost, etc, your fueling is much more similar to stock. the injector controller will fire extra injectors only when on boost (you hook up a pressure sensor). so you wont have to firm up the afm like crazy and shouldn't need an s-afc.
you'll have to install injectors somehow somewhere after your intercooler, like on the pipe over the block or something. you probably ought to use big injectors, between 2 and 6 of them i'd say depending on your power goals. it would be freaking sweet to put an additional injector per runner on the manifold. yeah man.
i was thinking about doin this but didnt want forged items in my 5m as i could easily make the power with a 7m with much less mods. but anyways basically this system makes you drive smoothly with the stock injectors but when on boost the 2 extra injectors open up and supplies the given fuel for the boost. you would hook this up before the throttle body and it must be welded on.
I found that about 6:1 was good for me, but as one noted, found it too lean. Since there are other tuning factors, the easiest thing to do would be to buy the Super FMU that is adjustable via a remote knob or another adjustable unit. I am running the Cartech and find it works quite well to adjust via a tiny needle valve. Some I believe are adjustable via changing out a disk but I haven't tried that type - seems pretty straightforward tho, just a little more effort.