It will depend on the dyno quite frankly. I would expect maybe a total of ~20whp increase with your basic bolt on modifications you had listed. On a 6speed g37s coupe with just a catback and tuning we saw right at 300whp. I believe the graph is posted on this forum actually in the tuning/dyno section. This was on a mustang dyno which tend to read 10%-12% lower than a dynojet style dyno.
Thanks,
Alex Goodwin
AlexG@motionlabtuning.com