I would start to set the K6-2+/570 at 6.0 x 75 (450MHz) at 2.1V Vcore.
If this is stable, you can try 6.0 x 83 (500MHz) later on, also at 2.1V Vcore.
Use these jumper settings:
CPU External (BUS) Frequency:
75MHz -> FS0: 1-2, FS1: 2-3, FS2: 1-2
83MHz -> FS0: 2-3, FS1: 1-2, FS2: 1-2
CPU to BUS Frequency Ratio:
6.0x -> BF0: 2-3, BF1: 1-2, BF2: 1-2
CPU Vcore Voltage:
2.1V -> VID0: 1-2, VID1: open, VID2: open
I don’t know if this board has an undocumented 2.0V setting, so use the 2.1V setting instead.
These settings are the same for a K6-2+ or K6-III+ CPU.
About the 83MHz Bus Frequency (FSB):
The maximum multiplier on the K6plus models is x6 so without overclocking the FSB you can run at 400MHz (6x66) tops on this TX97-XE. Usually, overclocking the FSB to 75MHz works fine on these i430TX boards, enabling you to reach a 450MHz CPU speed. Some people even got the FSB up to 83MHz for a 500MHz K6-2(+)...
The patched BIOS supports these 6x75 and 6x83 settings and will indicate the correct 450 and 500MHz CPU speed.
Maintaining stability when overclocking the bus above 75MHz on an i430TX system like this largely depends on the PCI devices used.
As you probably know, a higher than 66MHz FSB exceeds the chipset and PCI specifications, because the 430TX chipset uses a fixed 2/1 divider between the FSB and PCI bus clock. Normally, the PCI runs at 66/2 = 33MHz.
When running at 83MHz FSB, the PCI is automatically overclocked to 83/2 = 41,5MHz. This is a 25% increase above the norm.
Busmaster cards, like SCSI-Controllers or networking cards are especially sensitive to frequencies over 33MHz. But 37.5MHz (FSB 75) is usually oke.
So a CPU speed of 450MHz (6x75) should be oke but 500MHz (6x83) may give stability problems.
Note that running a K6-2+/570 at the 500MHz (6x83) setting will not damage the board or CPU but if it is not stable, it may corrupt the data on the harddisk...
Because the IDE ports are also PCI devices, the timing on the IDE channels is also 25% too high at 83MHz FSB. Modern ATA66/100 harddisks can take this but for a non-UDMA CD-ROM it may be too fast. But setting the IDE PIO mode in the BIOS on the CD-ROM channel to Mode 3 should help in this case (INTEGRATED PERIPHERALS menu).
Hope this helps,