Accelerators have different chipram speed access. So use one that gives you the full 7 MB/sec.. Bustest should show you the current speed. As meynaf wrote you need enough fastram. 2 MB might be a bit low.
Load/remap ROM to fastram makes ROM access as fast as fastram is. ROM speed is as slow as chipram.
Load everything to fastram instead of chipram if possible. The more chipram is used and fragmented the slower it is.
Use a graphics card to save chipram.
