Glenn D, closest I can come for comparison is a Meade S4000 SWA 18 mm in a members Orion 10" f5.6. How's that? Gave very nice O/A view. No app softening @ the edges. Should be O.K. in your f5. Worked fine in my f4.5.
L.
ps. Are the 5000's still 67 degs app fov?