As a film-biased photographer, I just wonder what tolerance there is for such things as the differences between frame proportions on film and printing paper. I reckon the key is whether or not you controlled the process. 35mm negative to standard print from an automatic system such as the typical D&P line isn't postwork. Hand enlargement, with that room to adjust the exact framing, is postwork. Safest to stick to the 6x4 printe, which will scan to plenty of pixels, and matches the negative proportions.