Martin, before you even start to think about new kit you need to learn how to use what you have already properly.
With the type of shots that you've taken, and in that light, the combination of a 450D & 55-250mm will produce pictures that range from abysmal, through adequate to excellent in the right hands. None of yours are abysmal, in fact in terms of composition, siting and timing they aren't bad.
Currently you are using the camera's Sports mode, which means apart from pointing the lens in the right direction and pressing the shutter at the right moment all the technical decisions are being made for you.
If you want to improve your photographs, the best thing to do before dashing out and buying new kit is to learn how to use your tools properly. That means understanding exposure, Depth of Field, use of focus points and a whole raft of other things.
There are plenty of guides on TP, both in this forum and the tutorial section. Once you are able to use the camera to it's full extent, there will come a time after some practice when you won't need to ask which lens to get, or how much it will improve your images, because you will already know - that's the time to upgrade!
Just to back up my point, with these photos an f/2.8 wouldn't have been much benefit at all because everything was shot at f/7.1 or narrower; ie you wouldn't have seen much, if any, benefit at all.
Put it this way, you wouldn't dive into a 20k Fell race with no prep and build up - at least not unless you wanted to be a passenger in an SAR heli! Photography's the same, except more expensive. You can throw all the money you want at it, but without the building blocks of knowledge your photos won't change a huge amount.
[/IMG]
