I've been successful with my 300mm Fuji lens on my 8x10 adventure so I am looking at something in the 400mm to 450mm range. I found a Fuji 450C f/12.5 and wanted to check with the group here to verify this is a good lens choice. It has plenty of image circle so that won't be an issue. I am wondering about size, weight, sharpness, etc.
As Mike said, go for it. It is a very desirable lens. Tiny and a good performer. Ground glass will be a little dark but the results you get with this lens will make you smile.
I would recommend the Nikkor M 450 over the Fuji- the fuji is do dim as to be nearly unusable in my opinion. But the Nikkor is much more manageable compared to the 480 Symmars and Sironars.
I use a Nikkor 450M on my 5x4 - in combination with a small top hat extension. I can vouch that this is a first rate lens. Its quite a heavy lens (compared to my others) but my Walker Titan can "take the strain" with ease.
I own both the Fuji 300C and the 450C. The two lenses look the same, you have to read the model to tell them apart. They both use the same filters as well. It's one of the three lenses I carry and it works great.
I'm in Burlington, Ontario if you want to try one out.