I’ve done lap the Lough which is a Sportive around Lough neagh, not a lot of scenery to be honest. There aren’t great views around the Lough, it’s just a vast expanse of water. Lot of the route is through areas such as the airport and the industrial areas and sand quarries on the edge of the Lough.
I’d recommend you do the Antrim coast road, Cycle from Belfast finishing at Portrush. Take a couple of days at it then get train from Portrush back to Belfast.
I’ll post up some websites in a minute but feel free to pm me. Give me more of an idea what you are looking for as well. Challenging hills? Pub? Tourist attractions?