The inducer by itself will not gain you anything on the top end. It may well help with your holeshot, but that's pretty much it. Now, it CAN indirectly help your top speed. A common application for the inducer is for guys who need to cut their impeller down to reach the peak HP of their motor. Typically when you cut the impeller down in a bigger boat, your launch/holeshot suffers. By installing the inducer, you can get back some/all of the low end punch, and when coupled with an impeller cut to reach peak HP, you may see an increase in top speed.
But before any of that can be speculated upon, everyone is going to want to know your current impeller make and size, WOT RPM, and the current top speed of the boat. With those variables answered, you'll start to get some meaningful information exchange.
Chris