There are some dynos of cars with just bolt on mods making 390+ rwhp SAE on a Dynojet. I have seen only one dyno of a car with just bolt on mods making 400+ rwhp SAE on a Dynojet, and it is not in the dyno database.
I would like to see more, but I think it requires higher octane so the ignition timing can be sufficiently increased. The only way to get that is with race gas or meth injection. That is why I bought a meth injection tune. I have not gone to the dyno yet, but have the usual bolt on mods like catless x-pipe, high flow filter, and underdrive pulley. The rear exhaust and fancy intake seem to be of questionable benefit so I do not have those.
Many people have reported smoother and more consistent power, and possibly a little more power, with a software update to the latest BMW software. Others have noticed better driveability from fresh spark plugs and a fresh air filter (BMW's maintenance intervals are questionable in the opinion of many of us).