The 2008 Evenrude 115HP E-Tech on my 175 has plenty of power. When conditions allow, I normally cruse 25MPH @ 4,000RPM. Max RPM is 6,000 for this engine. If new and operation cost is a factor, the 115 will burn less fuel/oil and initial purchase price is less. Last year Evenrude had purchase incentives on engine only purchases which included free digital guage package and an extended warranty to 5 years.
One advantage of the lighter weight of a 115HP engine on this size GW. I can stand in the corner of the stern without water coming in the self bailing scuppers. Of course, the extra weight of the trolling motor on the bow and full live well probably helps that situation, with any size motor.
Good Luck.
IN GOD WE TRUST
ORCA