I have a manualised re jatco behind my sr20 with a sequential shifter, it was built by bms transmissions and all i can say is i will never put a manuel in a turbo car again (unless holinger sequential).

For starters you dont have to spool up the turbo between shifts = faster car (i don't care who says it isn't, i have driven both manual and manualised auto in the same car and engine setup)

also as for downshifting it works fine just like the manual.

Keep the box oil cool and you dramtically increase the autos life ( i run a thermoed fan oil cooler with -6 lines)

I have 4.56s in the rear and the car happily goes 170km plus i think 4800rpm have not gone faster (was on race track)

as for price you can spend up to $5000 for a fully built box to handle 600 700 hp, mine was about $2500 with cooler and lines + shifter, next thing is built converter around $600, also for around $1300 you can manualise a jatco.

Hope this clears some things up.