Well, I isolated the problem in the old 2D code by making it write a log file of how long it took to carry out major functions, and the bottleneck was the DrawImage command. On some computers it took ages, on mine it was virtually instant.
I plan to do the same with this code to see if I can find the problem, although it'll likely just come down to the RenderWorld command (which doesn't really help). Still worth a try though.
Edit: I've made a little tweak to the code, removing the poly counter in the bottom left, which was using the Text command (everything else uses Vertices and Triangles). Which could be causing the issue.
I plan to do the same with this code to see if I can find the problem, although it'll likely just come down to the RenderWorld command (which doesn't really help). Still worth a try though.
Edit: I've made a little tweak to the code, removing the poly counter in the bottom left, which was using the Text command (everything else uses Vertices and Triangles). Which could be causing the issue.