I currently have a Nikon 90mm, Nikon 120mm macro and Schneider 150mm lens for use on an Ebony 5x4, and am looking at getting a longer lens ... but not too long, and not too heavy!

It's for landscapes rather than portraits.

I'm not sure whether 210mm is too near the 150mm to make very much difference, or whether I should go for a 240mm or even 300mm.

The Ebony I have is an SW45, but I also have the extension back, so have 270mm of extension.

I also (a complete impulse buy that I shouldn't really have made, but it was under 45% of new price and is pretty close to mint!) just bought on eBay an Ebony SV45TE, which has much more extension at 445mm.

I'm planning on keeping one of the Ebonys, but haven't decided which will stay and which will go yet. My hunch at the moment is the SW45 will probably stay, as it gives me an easier option of getting a 75mm (I'd have to change the bellows on the SV45TE I think), and it's lighter and looks easier to operate.

I favour Nikon lenses really, and have been following two 300mm F/5.6 lenses, but would imagine these are pretty big and heavy (I think they are Copal 3).

My budget is up to £400 ($800), and if used would want a pretty mint condition lens.

So any suggestions for the lens I should go for?

Thanks.