I think the 5" SCT can use slightly higher magnification. IMHO, you can use magnification from around 150x to 200x... 8mm to 6mm or 16mm to 12mm with 2x barlow.For planets & Moon, you can consider a 9-12mm ortho or plossl
Anyway, use the following formula to determine:
Magnification = scope focal length / eyepiece focal length.
True Field of View = Eyepiece Apparent Field of View / Magnification
Have a nice day.