So I'm replying without your post, so I will put my thoughts here:
1. Trust your gut on this one, your the expert in the problem domain, we're not. 2. As part of your argument I personally would prefer that it is at least tested in the context of an image library. We don't want any hidden problems there even if that is not your goal to implement the best image library. 3. Assuming pragma(inline, true) does in fact work, as long as the different operations are made simple I see no reason why it would be any less efficient, after all surely e.g. gdc/ldc can optimize and vectorize it?