Edit A1200_WHDLoad.conf or A1200_WHDLoad_window.conf (available via context menu for slave files).

Change 68020 to 68040. Maybe it will be enough.

For JIT (copy pasted from the readme):

cpu_speed=max
cpu_type=68020 (or 68EC020, 68040, 68060, see Known issues)
cpu_compatible=false
cpu_cycle_exact=false
blitter_cycle_exact=false
cachesize=8192 (or higher)
comp_constjump=yes
comp_trustbyte=indirect (see Known issues)
comp_trustword=indirect
comp_trustlong=indirect