Most impellers will improve one end and cost you on the other end. It is very challenging to improve the bottom end and the top end as your engine is limited on both horse power and RPMs. Unless you increase those, an impeller normally is not a great answer. There are some, Skat I believe, that do actually heals across the board. But mostly help within the normal range. So you may get a small increase in bottom end and MAYBE 1 or 2 MPH on the top end, but the mid-range will be better than stock.
BRP did a very good job in impeller selection relative the rated HP and max (limited) RPM.