Here are a couple of the shots taken in Petra, Giza and Cairo. For the cheapest option, the Sigma really seems to be a good option. Sharpness never feels like an issue, nor does low light. However, some thought needs to be given before each photo to ensure you have taken into account the warp that will appear at the edges, particularly in the corners. For some reason on my lens this is most evident in the top right hand corner.
The first view of the Treasury at Petra. It was truly an amazing sight.
Apparently the whole building was carved from the top down out of the mountain. Look closely and you will see a lot of design that in the UK is believed to be of Victorian origin.