Tamron SP 180mm f2.5 LD IF -vs- Nikon 180mm f2.8

Hello All,

I'm a relatively new Nikon user having just acquired a D600. I'm in the process of liquidating my Pentax and Canon inventories and building up my Nikon kit. I've got a question regarding one of my current lenses. I have a Tamron SP 180mm f2.5 LD IF Adaptall lens. It's a little bit of a rare bird with only 3000 copies being made.

I've got adaptall mounts for Pentax K and Canon EF. I could also pick up a Nikon mount, but I'm starting to wonder if I should replace the lens with a Nikon 180mm f2.8, though. The Adaptall-2 website lists performance of the two lenses and they seem very similar:

http://www.adaptall-2.org/lenses/63B.html

Based on those numbers, it seems like I'd be giving up a little lens speed and the "rarity" factor for autofocus. I was curious if anyone has every done a head to head of the two lenses, though? Any thoughts in general about the Nikon?

Thanks in advance for any help.

--
Chris
Denver, CO