RE: Engine selection for Nexstar ArF help
The Super Tigre G-61 would be very heavy for a Nexstar, but the G-45 ABC or G-51 ringed are both very good choices. The power output of the two is reported to be very similar, so you might save yourself $15 and go with the G-45 ABC if you choose Super Tigre. The Magnum XLS .46A is also a really solid value in the size range you're considerating.