On my site I use the setting that generates intermediate pictures with a fixed height of 600. This way the normal pictures always look good on a 'standard' resolution monitor. I have however a few panorama photo's that become waaaay to wide. Would it be possible to change the default setting to height = 600, but if a picture's width becomes more then 1000 then use setting width = 1000 for that single picture?
Seems to me that under the circumstances you specify (if width becomes more then 1000 then use width = 1000) then you will distort the aspect ratio of the picture. Most likely you will not like the result.