Lens Help?

Hey guys,

I have some extra money now to upgrade my lenses, and I've been looking at replacing my Tamron 17-50 with possibly a 17-40L. I'm aware that on my crop camera (60D), they're 2 different focal lengths. However, what I'm primarily concerned with is the image quality.
Is the IQ of the 17-40 L (specifically the color, saturation, as I've heard this lens is superb in those respects) big enough over the 17-50 to warrant an upgrade? Because I've been looking at reviews and comparisons, and apparently the 17-50 is actually sharper than the 17-40, and depending on the review, matches the 17-40 in IQ. So if the IQ difference is minimal, then I'll just keep the Tamron and spend the money elsewhere, perhaps on a different lens upgrade.

Another possible choice to replace the Tamron is the Canon 17-55. I know that this question has been beaten to death, but is the Canon really so much better than the Tamron as to warrant the price (almost double)? Again depending on who you believe, they have either basically equal IQ or the Canon soundly bests the Tamron. I'd like to get a final, definitive opinion on this before I take the plunge.

In addition to upgrading my primary walkaround zoom lens, I am also upgrading either my prime lens or 'telephoto' lens. I have a Canon 50 1.4 right now, and while I like the IQ, it's soft sometimes, the AF is just too inconsistent, and I've found the focal length to be a bit too tight. I'm looking at either the Sigma 35 or the Canon 35L to replace it. The general consensus seems to be that the Sigma 35 is a superior lens at a significantly cheaper price. Is this true? What matters the most to me for this lens is the quality of the bokeh (although general IQ is important as well), because that's the whole reason for this lens, at least to me
And I've found that I don't use my 70-300 all that often, and indeed don't really have much of a use for a telephoto lens. So another option is to replace it with a Canon 135L. I've heard great things about this lens, despite the radically different focal length.

I basically have enough money for two lens upgrades, so it boils down to:
which lens to upgrade? (walkaround zoom, fast prime, or telephoto)
and which lens to upgrade to?

For reference, here is my current kit:
Tokina 11-16
Tamron 17-50
Canon 50 1.4
Canon 70-300

Thanks!

what do you mean by "their two different focal lengths"?

the 17-40L will be exactly like using your tamron from 17-40mm...

as for the lens, i think it's about the worst choice you can make on a crop...get the 17-55f2.8 IS if you want to upgrade over the tamron...if you don't want to spend the money, look at the sigma 17-50mm f2.8 OS...

personally i'd look at the sigma 30mm f1.4 as well...if you're on a crop, why not take advantage of the great lenses that are designed for it, and also can save you a bit of money

check photozone.de for really detailed (super nerdy) tests of most lenses.

But for your current question, I'd get a lens with different focal length than what I already have, unless the one I have is giving me trouble.