Yes - for one processor *only* it is compatible - that is the Intel M 765 SL7V3 Dothan.
Why only this last processor of the 400 MHz FSB series (715, 725, 735, 745, and 755) has 32-bit PAE, NX/XD, and SSE2 enabled, is beyond me.
As a partial trial, I dropped in the 533 MHz FSB 780 SL7VB realizing that the higher FSB speed would de-rate the whole CPU in being forced back to 400 Mz. The "test bed" had the ATI Radeon 7500 GPU, 2 GB of high-quality RAM, 100 GB 7200 RPM drive (Travelstar)
In actuality, the T-42 did run with 780 and was "as slow as molasses". The BIOS is clearly not written for this type of situation. In trying to use the Win 8 RTM Upgrade Assistant, the system was failed as the hardware was too slow.
I then swapped that for the 765 and passed the compatibility tests quite quickly (I'm guessing several minutes).
So... final answer - only the last of the (715, 725, ... 765) series works and appears to be as fast, if not faster, than XP.
No, I have not formally benchmarked it. I did run CPU-Z and the readout appears as expected. I also ran CPU-ID's HW Monitor and CPU temp using Arctic Silver 5 thermal paste was 33 - 37 degrees C / 91 - 97 degrees F.
Three other thoughts:
1. Recall that the T-4x series was *before* the Windows key. You can simulate it with Left Control - Escape. Some have remapped the Right Control key to the Left Windows key scan-code 0x5B or the Right Windows key scan-code 0x5C (see for specs http://download.microsoft.com/download/1/6/1/161ba512-40e2-4cc9-843a-923143f3456c/scancode.doc
2. Classic Shell is a freebie that immediately gets rid of the Metro UI and allows you to choose between Classic, Vista, whatever, and restore the Start key (see http://www.classicshell.net
3. Fences is a great Desktop organizer that groups icons (see http://www.stardock.com