I managed 34mhz on a A3640 rev 3.2 with the delay line hack and a 33mhz 040 chip.
at the time i hadnt pushed it any farther(no faster osc's within reason),but it was rock stable and quite a diff. over the stock 25mhz.I used 60ns ram on the motherboard although this may not of mattered but its a safe bet.sold the 4000 to a toaster user years ago who really liked it.
I used a good fan and also heatsinked the hotter running pal's on the board just in case.
