If you're only going 10 miles on the freeway by yourself, either of these bikes will do it with room to spare. I've owned a 400 for a little over 4 years. I have the stock windscreen with stock Suzuki hand guards. Works great for what I do. I've worked on a couple of 650's. I'm all about cost per mile of ownership and power to weight. In these two cases the 400 comes out in front. Maybe you weigh 350, or you plan on riding cross country or do a lot of two-up riding. Then the 650 makes sense. Do you ride 10,000 miles a year? Do you have unlimited funds for maintenance? Are you buying brand new? Do you trade in every couple of years? 400 has a serviceable belt that is good for up to 20,000 miles. You hit 40,000 miles on a 400, you're on to your 3rd belt. Do this with a 650, and you know... What's the answer to your question? It depends. At any rate test ride them both. See if one talks to you.