Glass or new Body - current body Rebel XSI

I'm currently looking into purchasing a new body to upgrade from my Rebel XSI. I have a 24-70 2.8L lens that is my primary lens. I am looking at upgrading my body to a 5D MKIII or the new 6D, but I don't know if I should get a 70-200 2.8L IS instead. I think that I am at my limit on performance of my camera body.
Anybody have any ideas? Trying to see how much better my L would look on a 5D?

Personally, I'd upgrade that body unless you are really missing the long-end right now.

ask yourself what upgrading the body will do, its unlikely to increase IQ, unless you are going full frame.

if its better ISO, better AF, burst rates, etc, then yes upgrade the body, otherwise glass is your best bet.

If the 24-70 2.8L is the only lens you have (and I assume it isn't), then more glass...unless what you shot always falls in the 24-70mm shooting range (but I'd still lean towards more glass). The new body would be a nice treat, but without knowing what you are shooting, how you use the camera, your proficiency with the settings on your existing camera, etc, etc you won't be able to get much real help yet.

If on the other hand you have a good range of glass that suits your needs, then why not the body upgrade. Maybe you might care to share what you currently have and how you like to use it.

Keep in mind, the 24-70 will be shorter and wider on a FF than on your current body. That could affect your thoughts on having that as your only lens.

I went from XSi to T1i to 60D. There isn't a dime's worth of IQ difference between them. I think the XSi was better at ISO 1600 than the T1i was. Above that the XSi is out of the running. The 60D is about one stop better noise profile than the T1i. I like the ergonomics and controls of the 60D MUCH BETTER than those of the Rebels. I want to go up to FF, also. Right now I am between the 5D3 and 6D waiting on reviews of AF performance on the 6D.

I have a Canon Xsi also. I recently brought a 5D MARK II. And I LOVED IT! FF truely a GEm. However the 5d MARK II SUCKED in terms of auto focusing. The focusing speed is like the Canon Xsi or worst. Most of the picture i took are "SOFT"! Therefore I sold my 5d MARK II. I am looking forward for 5D MARK III until the price drop down to $2800. Right now it's at 3400 which is ridiculious over priced.

If I had the money right now or If i were you, I would upgrade to a 5D MARK III. Totally different experience. I would never go back to crop frame cameras. As for not i'm stuck with the Canon Xsi again with my beautiful 70-200mm f 2.8 L IS. Until they lower the damn price!

XSi -> 5D3?
Expect some brain explosion!

Body is your answer. Do a used mark2, save for the big gun lens.

I still use an xti, produces sweet images. Glass is always an improvement.

New 6D + 70-200 f/4L IS unless you need the low lighting.

FF requires good glass imo so i would say work on at least have 3 good lenses in the focal range you primarily shoot be it zooms, primes or a combination of those first, then upgrade.
That said you maybe the type of shooter who requires only 1 lens, so think about what you shoot mostly and if in FF the 24-70 is your normal shooting range then upgrade to a FF body, if you don't need a lot of features then the 6D will be fine for you.

I started with an XSi, then bought a 7d and more recently a 5dII. If I had gone directly from the xsi to the 5DII, I'd probably be really happy. Unfortunately, the 7d in the middle made it difficult to love the 5DII. IQ of the 5D is amazing, but the AF is primitive. The AF of the 7d is great, but the IQ is relatively poor. I'm in the process of selling all three of them and buying a 5D III. Hopefully it will be the best of both worlds!

If I were you, I'd probably wait for the 6D at this point.

I've owned an Xsi in the past, and now own a T3i. I feel like there is a fairly significant change in IQ. Perhaps it is due to pixel count for me because I crop often. Either way, I see a difference.

Kmccarthy, 5D MARK III is the way to go, Xsi has poor IQ and low focus. 7D has very fast focus but cropped body. 5D MARK II poor Focusing system which made most pictures "SOFT" and guess what 5D MARK III solved all those problems! ( but yet it's very pricey!)