I don't know what to tell you using weight designations for loaf size because I didn't find consistent answers to your question when I searched, so I would recommend measuring the inside dimensions of the pans and use the one closest to 9x5. I have used cheapo metal pans and glass ones with good results, but haven't used the disposable ones. It should work fine, but definitely set them on a baking sheet in case of butter overflow and also cover loosely with foil if it's getting really brown on top before 50-60 minutes of baking. Hope it turns out good for you!