I can't really help with either of the two scopes in question. I have looked through both the 85 mm Razor and the 50 mm Razor but not the 65 mm. I haven't handled the 66 mm Kowa either. But I would like to throw another option into the mix.
So, the Nikon ED 50 is too small and you don't want a full-sized 80 mm class spotting scope. That leaves the 60 mm class that you pulled those two scopes from. How about the Opticron MM3 60 mm? The 60 mm does 15-45x with the HDF zoom or you could move up to the SDL V2 zoom. Same magnification but slightly better optical performance in a few areas.
The reason I mention the Opticron is because I have compared the 50 mm versions of the Razor and the MM3 and felt that the Opticron was clearly better optically. If that is the case with the 50 mm models then I think the 60 mm MM3 would be a viable alternative considering the selling price (at Eagle Optics for example) for the MM3 60 with HDF zoom is $784 versus the $1199 for the Razor 65 mm.
Here is a comparison of the specs of these two scopes....
Vortex Razor 65.....
Magnification 16-48x
Objective Lens Diameter 65 mm
Body Style Angled
Field of View 138-75 feet/1000 yards
Eye Relief 20-18 mm
Close Focus 11.5 feet
Weight 48.4 ounces
Length 14.1 inches
Weatherproofing Waterproof/Fogproof
Opticron MM3 60 mm with HDF zoom
Magnification 15-45x
Field of view (feet/1000 yards)138 / 63
Eye Relief 22-17mm
Close Focus 11.5 feet
Eyelens diameter 24 mm
Weight 33 ounces
Length 12.7 inches
Weatherproofing - Waterproof/Fogproof
Compare those with the Kowa 66 which retails for $1258 at EO.
Kowa 66 with SV zoom eyepiece
Magnification 20-60
Field of View (feet at 1000 yards) 99.75 - 52.5
Eye Relief 16.5-16 mm
Close focus 18 feet
Length 15.1 inches
Weight 45 ounces
Weatherproofing - Waterproof/fogproof
For further support of the MM3 60 mm suggestion, here is a review on it by an independent reviewer......
http://www.bestspottingscopereviews.com/OpticronMM360GAEDTravelscope-16.htm
And if you want to see what type of image quality it can potentially produce then here is a pic I took with it and my Iphone 6S....