> So at least if you still are using your mainboard memory, you're in trouble.
 
 Yes, I still have 16MB on the mobo.

> Please apply the appended patch to sys_machdep.c. It will force the mentioned
> functions to always use line-sized flushes.

cc  -Werror -Wall -Wstrict-prototypes -Wmissing-prototypes  -Wpointer-arith -Wno-uninitialized -Wno-main -O2 -m68060 -Wa,-m68030 -Wa,-m68851 -msoft-float -I. -I../../../../arch -I../../../.. -nostdinc -DM68060 -DM060SP -DLKM -DDIAGNOSTIC -DKBDRESET -DSERIBUF_SIZE="0x1000" -DSEROBUF_SIZE="0x200" -DLEV6_DEFER -DMAXUSERS=8 -D_KERNEL -Damiga -DFPCOPROC  -c ../../../../arch/amiga/amiga/sys_machdep.c
../../../../arch/amiga/amiga/sys_machdep.c: In function `cachectl1':
../../../../arch/amiga/amiga/sys_machdep.c:145: invalid lvalue in assignment
../../../../arch/amiga/amiga/sys_machdep.c:145: syntax error before `;'
*** Error code 1

 Which is understandable, because my config file defines only M68060,
 not M68040 (is that wrong?). In that context, this code fragment looks
 just wrong to me:

                if (addr == 0 ||
#if defined(M68040)
#if defined(M68060)
                    (cputype == CPU_68040 && req & CC_IPURGE))
#else
                    (req & CC_IPURGE))
#endif
#endif
                        doall = 1;         <--- line 145

 It should be 

                if (addr == 0
#if defined(M68040)
#if defined(M68060)
                    || (cputype == CPU_68040 && req & CC_IPURGE))
#else
                    || (req & CC_IPURGE))
#endif
#endif
                )
                        doall = 1;

 Btw, I'm still on 1.5.1.

 There appears to be some improvement. I started a download via scp and
 a kernel compile, and the download does continue - mostly. Looking at the
 modem leds, it sometimes stalls for a few seconds, but then continues.

 But it does that even without cpu load, although the stalling periods
 are shorter.

 Should I recompile the kernel with M68040 enabled? With M6840 enabled,
 but not M68060?