There are contexts where 4G speed is nice to have, and contexts where it is essential. The Luggage-Free experiment definitely falls into the latter camp.
I've been lucky to have a borrowed Telstra 4G SIM while I've been roaming the country. Where the difference has been really obvious is in uploading videos. That has been a slow process when using Wi-Fi (as I had to in New Zealand), but much faster on 4G. No exaggeration: one video went up so quickly I thought the upload page status was in error.
In most other contexts, 3G is ample; after all, my day job mostly involves dealing with text. But speed on the network plus speed on the Z10 is a nice combo.