I found a way to get 133 Mhz Frontside-Bus in the Thinkpad 770X (tested), 770Z (tested) and 600E (not tested, but should also work because it uses the same clock generator). To achieve this, you must desolder the original clock generator (PLL) on the system board (IMI SG577DYB) and solder a new one that has the same pinout but provides more frequencies. I used the ICS 9248BF-55 which can be found e. g. on Gigabyte GA-6BXE and GA-BX2000 desktop motherboards. This clock generator provides 66, 100 and 133 Mhz FSBs @ 33 Mhz PCI clock (works), 75 and 112 Mhz FSBs @ 37 Mhz PCI (worked for me, too) and 83 and 124 Mhz FSBs @ 41 Mhz PCI clock (not tried, but should most likely cause problems).
Because the i440BX chipset in the notebook can only provide 89 Mhz AGP clock at 133 Mhz FSB (which is too high for the Trident graphics chip) you have too feed the AGP clock with a second clock generator and configure its FSB outputs to 66 Mhz at 3,3 Volt operation (and use it for AGP). I do not know if the Neomagic graphics chip in the 600E works with 89 Mhz AGP clock but if it does, it makes things a lot easier.
To make thing even more difficult, you have to use PC133 CL2 (not CL3!)
SD-RAM SO-DIMM for stable operation because the 770X and 77Z do not provide an option in the BIOS to set the CAS-latency to 3 and therefore only support CAS-latency 2.
I do not know if 600E supports CAS 3.
256 MB-Chips that run CL2 at 133 Mhz and are compatible to i440BX chipset can be difficult to get, the crucial ones which are listed as comatible for 600X do work.
With this mod, it should be possible to overclock 850 Mhz MMC2-CPUs up to 1133 Mhz but you can of course also overlcok chips with lower mutliplier e. g. 450 Mhz to 600 Mhz.
The higher FSB should have a bigger impact on performance as the higher processor clock because the Frontside-Bus is the bottleneck on the Pentium III.
For example, a 600Mhz Pentium III at 100 Mhz and multiplier 6 is much slower than a 600 Mhz Pentium III at 133 Mhz FSb and multliplier 4.5.
Since I own the µPGA2 to MMC-2 socket adapter, I can also use CPUs with multiplier 9 and 10 in the newest D0-stepping which usually overclocks good. MMC2-CPUs are only available with multiplier up to 8.5 and in the older C0-stepping which can still be overclocked to 1 Ghz+, especially when raising Vcore (voltage can be raised and lowered easily on MMC2-processors, I will post information at another time; it helps to save battery-time and make cooling easier when lowering the voltage).
850 Mhz >>> up to 1133 Mhz
800 MHz >>> up to 1066 Mhz
750 Mhz >>> up to 1 Ghz (should always work without raising Vcore).
The 1 Ghz µPGA2 CPU was not able to run at 1,33 Ghz (133 x 10) even at 1,75 Volt (Vcore can be adjusted with switches on the socket adapter).
A 900 Mhz µPGA2 CPU was able to run at 1,2 Ghz at 1,75 Volt, but I still have to test if it is stable and if the voltage can be lowered to 1,7 Volt or 1,65 Volt
Even if it does not work, 933 Mhz (FSB 133 and the mutliplier 7 of the 1 Ghz CPU in the battery-optimized mode should be faster than 1 Ghz @ 100 Mhz FSB and mutliplier 10).
933 Mhz was also stable on my old 850 Mhz MMC2-CPU without raising voltage.
Unfortunately there is no 950 Mhz µPGA2-CPU, so I can not test 1266 Mhz.
This mod is only possible with good soldering skills and equipment and does not make any sense regarding cost/performance (maybe only when using a 450 Mhz CPU because it can still run with the original CPU cooler/fan assembly at 600 Mhz); it is only proof-of concept
Here are some pictures, but they are 150KB each, so be warned!
backside of system board with switches
These are far more complicated because I made a circuit that changes the FSB when AC-adapter is plugged in. Normally, only three simple switches connected to ground and to the three frequency-select-pins of the clock generator can be used to set the FSB.
topside of the system board with the new clock genator ICS 9248BF-55
topside of the system board with the second clock generator to feed the correct AGP clock
screenshot at 89 Mhz AGP
This happens if you do not feed correct 66 Mhz AGP clock when runnig 133 Mhz FSB on the 770X and 770Z. The graphics chip can not work correctly with this high AGP speed. Maybe the Neomagic graphics chip on the 600E can.
850 Mhz MMC2-CPU running at 933 Mhz (7x133 Mhz) and correct AGP clock feeded.
900 Mhz µPGA2 CPU running at 1,2 Ghz and correct AGP feeded
Memory that works at 133 Mhz and CL2
Selled by Crucial for Thinkpad 600X, manufactured by Micron.