I recently came across this app. that may help out some of you who use the GO64 mode of your Commodore 128. The program provides you with some helpful shortcuts for some floppy disks tasks (like formatting and copying files between disk drives). But, the major feature of the program is to speed up the loading of C64 programs, kind of like turning your C128 into a fast loader for the C64 mode. It uses the C128's "burst mode", if you are using a 1571 or 81 disk drive, to speed up the loading process. Then, the program automatically switches you 64 mode and runs the program that it has just loaded.
If you're interested, I've done a more detailed review of the program on my blog, here: LINK