As Nike1200 mentioned, in most cases if you gain on the bottom end you lose on the top end relative to changing the impeller. The times this is not accurate is, when you can increase the engine RPMs over what they were (factory) and or add items to the engine to increase its power.
So, in your case, the tune plus an impeller would likely be a good combination. [MENTION=2]hfgreg[/MENTION] would be able to confirm my though process as he has good knowledge pertaining to the tune you obtained.