I want to start upgrading my lens kit, so that one day when I can afford a 5D Mark III (a few years from now) all I will need to do is get the body. In the meantime I want to drop my EF-S kit lens for a quality replacement.
Would the Canon 17-40mm f/4 L EF be a good option for replacing a 18-55 EF-S kit lens for a crop body? When I eventually go full frame I will want a wide lens, so I thought this one may serve that purpose while also being a good replacement for the kit lens on a crop body.
I was going to upgrade my Rebel XT to a 7D about a week ago, but then the rumors of the 70D announcement started coming. So for now I'm holding off and waiting to see what this new camera will entail by the end of the month before deciding which camera body to get.
I did the exact same thing when I got the 17-40 for my 7D - I had sold the 18-135 kit lens - all in the hope of going FF someday.
TBH, I hated the lack of focal length on the 7D as the focal length was neither here nor there. I cursed myself for not having purchased the excellent 17-55 f/2.8 IS which would have given me a full stop of light and a couple more stops in IS which could give me shots at ISO 800 which were possible with the 17-40 only at ISO 3200+ (useless on the 7D).
Subsequently, I did go FF last October and had an equally frustrating time with the 17-40 on the FF. the constant f/4 aperture on the FF was useless because the IQ isn't something to rave about unless you stopped the lens down all the way to f/8 or more.
Frustrated with the 17-40, i finally sold it today.
Cutting the chase ... Do consider whether the 17-40 is that great a deal on the FF and worth ignoring the excellent EFS 17-55 IS. Don't get entangled in this whole business of going FF someday. You can only shoot with the equipment you have in your hands ... Not with what you expect to buy someday.
BTW, the 17-55 is one lens which retains its value. You can easily sell the lens on eBay for a very nice price when you do go FF.