Well, not sure if you travel in F internationally but you certainly know that some airlines like Lufthansa (reportedly the biggest carrier, is that true?) have a single item rule AND a 8kg limit. So if you plan to go really with a SINGLE bag to hold, I quote:"laptop, DSLR, up to two lenses, books and clothes for up to three weeks without washing", then you have two problems. The first is the weight problem because those ingredients alone will get you to the 8kg limit when you haven't even finished packing. Some airlines (Virgin for example) have a 6kg limit. If you add 2.5kg or so for the bag, you can just forget about it. The second problem is that it will be hard to fit that packing list in even the biggest of those bags. You will also need some padded lens sleeves because none of these bags offer enough protection. The bulk of laptop and camera equipment alone will make the rest of the packing very impractical.

Sorry to be so skeptical but I'd go over the packing list, the travel plans (including luggage restrictions) and the airlines again before I even spent a single dollar on something that might turn out to be a crapshot.

In that sense, why not get an Outdoor Products Essential Carry-on (short OPEC) or an ebags weekender and try it out first. The OPEC is under $40 and gets really nice press as you can see on practicalhacks and OBOW. It is also one of the lightest bags which is of utmost importance if you want to pack anywhere close to what you said and still fly on non-US airlines where they have much harsher carry-on weight limits.

Till