I purchased a 7D a year ago along with an 18-200mm. Most of my current photography is outdoor daytime shooting sports (kids soccer and football) and the 18-200 was fine for that. I want to become a better photographer and eventually into an occupation. I like the 7D for the 8fps which was my biggest sway when deciding on the 5D Mark II at the time. I know the 5D Mark III now shoots up to 6fps but that cost is down the road. I foresee the future as keeping the 7D and adding a 5D III.
I took photos last year for a friend who's daughter celebrated her quinceanera with the 18-200, shots in the church and outdoor were fine but I spent hours in Lightroom trying to recover the banquet shots, especially when they lowered the lights and I had to crank up the ISO. I know that is a result of a poor f-stop lens so I saved up some money and sold the 18-200 in order to purchase a better lens. At the time I was deciding on the Sigma 70-200 2.8 and the Canon 70-200 f/4. I opted for the Sigma just in case I needed the 2.8 speed for evening or indoors and it already had a lens ring. I realize that isn't a big deal but I have a Manfroto monopod with a ball head that I use for the sports and like that the Sigma ring disconnects easily to go back to hand held without having to remove the lens. Considering the purchase of the Canon f/4 and no lens ring I was worried that all that forward weight with the monopod mounted to the camera body would wear heavily on the ball head.
I also bought a Canon 50 1.4 along the way for indoor portrait work. I really like to shoot without flash and this lens has been great. This gives me an 80mm lens on the 7D.
My dilemma is I've purchased a number of machines from Dell recently and have $1000 in Dell e-cards which can only be used on their site. So I'm looking at the lens options they have to offer.
First two options I'm looking at would be to sell the Sigma, on eBay they seem to be going for $700 on average. Buying either the 70-200 f/4 for $1199 or biting the bullet and getting the 70-200 2.8 II for $2399 (both before applying the $1000 Dell ecard).
The left brain right brain debate is if it's worth losing $500 on the Sigma (bought it for $1200 in Feb 2012) to sell it and buy the 70-200 2.8. If I buy the 70-200 f/4 and sell the Sigma I'll actually be up $500 (f/4 would cost me $200 net from Dell) that could be applied toward another lens.
The other options are to keep the Sigma and either get:
1) Canon 24-105 f/4 for $1149 ($150 after Dell card), reviewed as a great lens and would be compatible with FF when I eventually get one, would be 38.4-168mm on my 7D now.
2) Canon 10-22 3.5-4.5 $759.99, would only be useable on 7D (AF-S lens) but nice to have/learn an ultra wide (16-35.2mm on 7D). Along with the 17-40 f/4 which would be FF compatible and offer a 27.2-64mm on the 7D. Both lenses would end up costing me $500 but give me a pair of lenses covering 16-64mm, my 50mm Canon, and the Sigma for the 112-320mm range.
3) 3rd option is Sigma 10-20 4.5-5.6 for $479 also a crop sensor lens only, along with the Canon 17-40 f/4. Is the Canon 10-22mm worth the $280 difference?
I know it's not the equipment that makes the photo as much as it is knowing how to frame the shot, get the settings right for optimal exposure and so on but I also know good glass makes achieving good shots easier for us newbies 
Any suggestions are welcome. This certainly won't be the last time I purchase lenses I just can't decide if the difference going with Canon's flagship is worth losing as much as I would by selling the Sigma or if the f/4 Canon will be better than the Sigma.
Going the other route and keeping the Sigma, I've read a lot of great reviews for the 24-105 but they generally are shooting with FF bodies. The purchase would either be that one Canon 24-105 or a bundle of two lenses in the lower focal range to open a new area of photography I haven't been able to try.
Great my headache is back now, thanks for reading.
