Hi Pipe,
The speed difference between the Atlin and Telkwa is not much. I have only tested it a little bit with GPS on a lake, but it seems like the Atlin is about 10% slower (less than 1/2 km/h difference). On rivers, speed is less important because the river does most of the work for you.
If the packraft’s length is critical, you can make the stern (tail) a bit shorter and less pointy by simply rounding the tube pieces more before adding the final seam strip that joins them together. On the Telkwa you could do the same on the bow (front).
I have sent only a few packraft kits to Spain, and I don’t recall where exactly. I hope you can connect with someone though!
Feliz año nuevo!