I’ll say it again,

I think it’s better to stick to a 300mm for 4x5 in the field. But if your photography is such that you absolutely cannot tolerate something that short, then for the Chamonix I would recommend the 400T, you can use it without extensions and with shorter bellow draw, and so you will get good shots most of the time if you’re careful. Just suck it up and carry the weight.

Don’t spend more than the cost of a 4x5 Chamonix on a 450C lens that you need to operate with a long top hat or a long bellow draw with extensions. You will likely be disappointed with many shots because of the loss of stability.