An early draft of a track I made, Momentum X, was a huge lag monster because all the banners in it used one 256x256 texture each. This had to be fixed or the track would be useless, and reducing the texture sizes to 64x64 was out of the question because they looked like crapola. And removing them took too much away from the tracks overall feel. So what I did to fix the problem was to reduce the bin models graphic only slightly so I could fit several banners onto a single 256x256 texture, then with a simple remap in binedit (signs are a very simple remap in binedit and a great way to get started mapping if you've never done so before).
This's an example of what I did for another similar project.
In that particular texture above I could have easily fit one more banner by removing the wood area and reducing it and remapping it to a 64x64 since that detail isn't such a big deal.
Good luck with your project and if you have any questions or need a hand with something let us know.