I was considering this until I learned the 180mm Dome $1050 + N85 to N120 port adaptor $420 + zoom gears $200 +$175 = $1.8K? on top of the $1300 lens.
I know. I have it all. ;-)
For the 8 mm:
Total 1255,- I also have that. :-p
If you exclude the ability to zoom the difference is 1255 vs 1600. But as I said the 180 mm is far easier for over/under shoots. But the 140 mm also improves much over the smaller plexiglass versions which are almost impossible to use in that regard.