Free: Contests & Raffles.
Your issue seems to do more with lenses than with your camera body. I'd suggest looking at the Canon 7D. It's still a cropped frame but handles very high ISO really well. "Faster" lenses will also allow you to shoot in lower light conditions, giving much better results.
All Canon crop sensors are noisy and not good in low light. The 7D is really really noisy and produces ugly images, IMO. If you can shoot at ISO 200-400 all the time I guess it's ok, but if you are shooting in that much light then you don't have very good quality light. A new 7D is coming but now they say next year. I went full frame years ago after my 3rd 7D and I finally realized I hate the camera despite the great specs on paper.
Going from your current camera to a 5D3 will incrementally help you more than about any glass you can buy.
If you don't need fast autofocus, what's wrong with the 5D2?
Well I have the hood, caps, a Hoya multicoated UV filter ($50), a B+W XS-Pro Kaesseman circular polarizer with multi-resistant nano coating ($175) as well as the original instruction manual. Lens is in perfect shape. Glass has always had a filter on it. I want to sell it all together as I will have no use with $200+ worth of filters without the lens. Not planning on a 77mm lens in my new setup. I sense a classified ad in our future
Funny: i'm at the same place here I'm at at the XTi. Noise is mostly invisible < ISO 200 somewhat visible at ISO 400 and prominent at 800+. As I said 2/3 of my shots are great and that should be good enough for most shooters and impressive with a camera that I will likely sell on Craigslist for $200. I'm getting more bothered by the 1/3 shots where I want better ISO/noise performance.
These are ISO 3200 shots I couldn't get as good without this camera:
Having more focus points helps because you need them on the power points and the other point layouts from other cameras don't quite reach the power point. If you feel there is too many, you can simply change the settings to the diamond pattern or link them into groups for quick changing. The diamond layout is why I didn't like my 40D and some other cameras...
I know the 6D only uses SD cards and I'm not sure how quick those are. I think the U ones are faster now but I haven't compared them. I can download thousands of images in just a few minutes with the Lexar 1000x CF card and it saves me time at the end of long shooting days. The burst rate is also great for when you need to shotgun some shots off. Stay away from the original 5D. The battery life is awful and you have to change a few times each cold morning and always carry spares. It's too big a pain.Swap that 17-55 with a 17-40 if on a budget or 24-70 f4 (new version is amazing) and you are good to go.