The high colour .jpg image is going to be the issue here. You can get nice results with even a 16 colour workbench.
Check out the awesome work in this post over at EAB:
http://eab.abime.net/showthread.php?t=51657You don't have to strip right back either, you can play with 64/128 for example and still get great speeds.
There are other ways to get faster booting too like having a custom rom made up and getting rid of the reboot.
I suggest starting with a fresh workbench and building it up yourself, you could keep that old one as a backup and then you could build you own to your own spec.
If you want somewhere to start, check out the Classic Workbench packs as they are a great base to build on:
http://classicwb.abime.net/All the best,
Steve.
