Standard range glass for a FF & Crop pair

I'm well on my way to getting a 5D2 next, as its larger resolution, shallower DOF, and other FF perks are really beneficial to my kind of shooting. I'm planning to keep my 40D as a complimentary camera.

My Tamron 17-50 recently broke, so I'm left with a hole in my lineup. Should I get a standard zoom for my 40D (looking at the Sigma 17-50 OS), or get a standard zoom/prime that can also work on FF? Although the 24-105 has IS and the 24-70 as f/2.8, the Sigma or Canon 17-5x has both.

I was craving for L primes once I get my 5D, but now I'm rethinking whether I should stick to a zoom for the standard range because I can go from wide angle to short telephoto quickly. Or maybe I should just get a 35L and call it a day?

I shoot mainly portraits/studio, landscapes, and street photography/candid. No interest in sports, wedding, or wildlife.

What would be the best combination to support a FF/crop setup for my type of shooting?

Current lenses:
Sigma 10-20
(standard lens?)
70-200 F/4 IS
Sigma 85mm

Might as well get the 5DII + 24-105 kit. For the added price, if you don't like it you can sell it for about what you paid for it, probably even make $50 or so.

Cheaper solution: EF 28-135 IS. So many were sold in kit with 40D and 50D, these are widely avail. lightly used for $300 or less (I paid $250 w/hood & 72mm B+W UV MRC, all like new, shipped). It's an older design, sure... but IQ is good, build is decent, it's got USM, close focus and IS. I often recommend it and use one myself as a versatile walk-around lens and backup for my 24-70/2.8.

Less cheap solution, the 24-105 in the kit with 5DII is a good value. Build quality is better, so is dust sealing, but you won't notice much image quality diff. If you keep it and use it, turn on Peripheral Lighting Correction on the 5DII... otherwise you'll see fairly heavy optical vignetting in the corners with this lens at 24mm (this doesn't show up very much on crop cameras).

If you are using studio strobes or any sort of manual flash, the constant aperture of this lens might be preferable, over the variable of the 28-135. (Though some pros use that lens a lot for studio work and don't see the need for the much more expensive L: www.farace.com.)

As to using it on your 40D, a lot of folks say 24-whatever or 28-whatever lenses aren't useful on crop cameras. I disagree. I find them a great walk-around solution.

Pair any of those lenses up with an ultrawide zoom specifically for your crop camera if you wish... maybe a Canon 10-22 or Tokina 12-24, for example. Oh wait, you've already got 10-20 Sigma... so just hang onto that.

Eventually you might want a wider lens for full frame, too. I just use a Canon 20/2.8 and am happy with that.

And I have 12-24 for crop, which even thought it's designated "crop only", will fit and work on 5DII as wide as about 18 or 19mm before it starts vignetting. I've tested it.

However if you shoot a lot of landscapes and such with wide angle, you simply might want to use the FF camera most for that. Certainly it will be the best choice if big enlargements with lots of fine detail and DOF from here to eternity are your goal. If so, perhaps let the crop UWA go and get a wider solution for the FF... 17-40/4 is popular and relatively affordable solution. And just use the 40D for more telephoto stuff.

If you are planning to get some primes anyway, might not need an f2.8 standard zoom, too. Only you can say. There are the more expensive Canon 24-70, as well as Sigma in similar range, and Tamron that's close. AFAIK, both the third party lenses are FF capable (I know the Canon L is).

I'm totaly satisfied with Tamron 28-75 2.8 on 5Dc and it works OK on 500D. I'm very happy with 500D and Tamron combination for portraits.
Never miss IS on it. It renders good colors and sharp wide open.
28-75 and 70-200 F4 IS are the same for front thread size. I need only one CPL.
And it comes with six years warranty.

For the price of 35L you could get Tamron 28-75 2.8, Samyang 35 1.4 and Canon 1.8.

Thanks for all the comments so far. I love my Sigma 85mm and can only imagine what another prime can add to the fun in my shooting.

I would like to add a standard zoom to my lineup since zooms and primes both have their place, but I guess the main debate I'm having is whether to buy a standard zoom dedicated to APS-C (Sigma 17-50), or buy a zoom that can be used both for FF and crop.

A standard zoom is much cheaper on a crop though.

I've never tried the Tamron 28-75, but I might just give it a shot.

I found this doing a search as I was about to start the same thread. I have a 7D and just got a 5D2. I own a 24-105, 70-200 f/4L IS, Sigma 30, Canon 85 f/1.8, and just ordered a Sigma 50. As the 50 should be the same on FF as the 30 is on the crop, I'm debating dumping the 30. I don't think I'm going to make any changes with either of my zooms. The one area I am debating is adding a 100L Macro or a 135L. I think I'm going to want a 135L with the 5D2, as lately the 85 has lived on my 7D.

For the past several months I've been itching to make changes in my lineup but couldn't figure out what to do. Getting a FF body is like getting 4 new lenses! I need to explore each all over again and decide how each piece of equipment will be used going forward. I am also likely going to sell my P&S. Now I'm looking at possible $800 (that I should put towards the camera body) and I'm most of the way to that 135L!

I would skip getting a crop zoom. If you think in reverse, that 24mm will feel like 15mm on a crop. I plan to start out using the 24-105 on my 5D2. I don't doubt I'll still have the 85 on my 7D a lot. Also, where I didn't use the 70-200 much on my 7D, I think it might live on the 5D. I was struggling a bit with the combo this weekend, then I slapped the flash on and it got better. Then I stuck my home made bounce card on and I was getting some winners!