You should check out/search Megs threads on the Leather Spy Bag, it should answer most of your questions. I have the Lambskin Spy in Cognac, so I don't know if it is the same as the one you're interested in? I believe it only comes one size, the measurements are 15"w x10"l on the Leather Spy.
i have one in black nappa leather. The SA in NM told me there is only one size available for spy although they do indicated it as a medium size. However, to me this bag is really roomy, about the same space as my Hermes garden bag. The nappa leather is very soft and buttery. It is in fact not that shiny. Since I also have a chloe paddington, so if u compare the two, i would say the leather from spy is softer and with more bubble kinda like texture and not as shiny as the paddy (although i don't think paddy is that shiny after all). Hope this helps~~~