Trunk comparison: Fiat Panda vs Skoda Superb Wagon

Main Results
The Škoda Superb Wagon offers significantly more cargo space in length: with the seats folded down, the trunk is 40.2 in (92%) longer and with the first row upright, 20.5 in (96%) longer than the Fiat Panda.
The Fiat Panda's notable advantages lie elsewhere: the trunk depth (loading edge to trunk floor) is 3.9 in (125%) greater and the loading edge sits 3.9 in (17%) higher above the road than on the Superb.
The width at the narrowest point is the same for both models; the trunk opening of the Superb is only 2.4 in (6%) wider than the Panda (not a relevant difference according to your guideline). The height of the opening is 2.4 in (7%) greater on the Panda (also under 10%).
Impact on Usability
Škoda Superb Wagon: Due to the significantly greater loading length, the Superb Wagon is clearly better suited for long items (e.g., slats, long furniture parts, skis) and for larger luggage volumes relative to vehicle length.
Loading longer packages or transporting bulky cargo that needs to be pushed deep into the cargo area is also much more practical with the Superb.
Fiat Panda: The Panda has a noticeably deeper interior behind the loading edge and a higher loading edge above the road. The greater depth means there is more vertical storage space directly behind the loading edge — this is advantageous for stackable or bulky but not necessarily very long items.
The higher loading edge makes lifting heavy loads into the vehicle more strenuous and less ergonomic; at the same time, the higher opening height (under 10%) can slightly ease loading very tall items, but this is not a major difference.
Common Limitations: The narrowest width is the same for both, so there is no advantage or disadvantage for very narrow or unusually shaped loads. The slightly wider opening of the Superb (6%) is practical but not considered a significant difference according to your guideline.
Conclusion: For long or bulky transports, the Škoda Superb Wagon is clearly better suited. The Fiat Panda scores with a deeper cargo area, is more suitable for compact, stackable freight, but is less comfortable when handling heavy items due to the higher loading edge.