Generally - the larger the cams, the more revs are needed to get the engine to make power e.g at set of 280deg 11mm lift cams on an RB25DE would need 4500-5000rpm before it started to make power, below that the airflow through the ports is very slow and inefficiant, So you then need to rev the engine harder eg 9000rpm redline in order to have a decent power band, if the engine only revved to 7000, you would only have 2000rpm where the engine makes any grunt, so each time you changed gear you would drop out of the power and go no where.
Think of big cams like you would a big turbo...kinda