I thought you said you tested the 17-40 and already had the lens in question and found it superior than the 17-55 in "every way"?
I already own a 17-40mm. After extensive testing and comparison I found it to do significantly better than the more expensive 17-55.
in the 17-40 I didn't notice any barrel distortion what-so-ever. ... I'm not sure why someone would see barrel distortion on that lens.
I've noticed the lens distortion as well.
Ok, enough of wordsmithing.
The f/4L is not enough, however I'm not sure if I should sell it and go with the 17-55mm or just grab a 10-22 for wides and something in the middle later on.
I stand by the statement that the 17-40mm is not an ideal lens for use on a crop body, and that for most uses, the 17-55mm is superior. But the question is, in what way is the 17-40mm f/4L 'not enough' for you. Not wide enough? Not fast enough? If it's not wide enough, the 10-22mm is a good choice, as is a Tokina 11-16mm. If it's not fast enough, f/2.8 will likely not be enough of an improvement, and you'll need to start thinking a fast prime like the 50mm f/1.4 that you already have. If you need fast and wide, that's a problem on a crop body (and while there are solutions on FF, they aren't cheap).
The other solution is to add light, via flash, monolights, etc.
I've had issues with shooting in the shade (forest) and high isos. I shot in the grocery store at 3200 iso and I swear it looked like some kid was taking crayons and stabbing it all over (that's how grainy and pixelated it looked at the iso). I'm not sure if it's the lens or the camera or if I'm doing something wrong.
The lens does not affect ISO noise, except indirectly (i.e. f/4 is narrow, meaning need to boost ISO more often because your lens is slow).
Personally, I don't like the ISO noise of the 7D, and I really try to keep it at ISO 800 or lower. But, sometimes you need to go higher.
Suggestions would be 1) Shoot in RAW and 2) get something better than Canon's DPP for RAW conversions. Personally, I find that DxO Optics Pro does a much
better job at NR than DPP or Adobe Camera RAW. DxO also does a great job of removing the barrel distortion you're now noticing, without sacrificing sharpness. If you want to stick with Adobe, there are plugins like Noise Ninja and Topaz Denoise that will help, and are also superior to DPP.