In terms of use long term, not speed wise
My main point for getting the Kindle 3G is because of it's wireless 3G capability- I do a *hefty* amount of online reading as in 6-8rs a day (straight, constant use). multiply that by 5-6 days a week, year in year out that seems like it might "stand out" in terms of bandwidth usage over 3G.
I am weary of any potential "glass ceiling" that I may cross over. No shady hanky panky here, but I would be using the browser over 3G way, way more than the books storage capability.