why Im going for the 17-40 f4

The only one out of the 4 that makes sense is #3. Sorry but #1 and #4 are just silly. And 300 bucks is 300 bucks. LOL

And photozone's MTF charts between the 17-40L and 17-50 are almost identical.

17-40 L is a great outdoor lens. if you have fast primes to cover for low light, i dont see why not.

but if you're on a budget, like most of us do, and you want the best overall value for what you pay for, i'd say the tamron is the better choice. gives you greater focal range, faster across the L's focal lengths and if you find a good copy, the IQ may give the L some decent competition.

getting the tamron would cost a little over half the amount of money you'd spend on the 17-40L + 50mm 1.4 combo and give you great value. but money aside, i'd go the L too. add an 85mm 1.8 to the combo, and wow, what a great set to take pictures of people!!