I'm not sure that it negates the L2 cache issue. One of the issues with the motherboard L2 cache is that its presence can slow the maximum bus speed achievable. If you're going to run your G4 at a standard 50 MHz or below, this is unlikely to matter. If you're going to push the bus speed, then it could matter.
Apparently, removing resistor R31 on the 9500/9600 disables the L2 cache on the motherboard, so that is a route one can take if one does not have a Kansas board. I would double check my resistor designation before trying this. I'm flying on memory alone here.
Most CPU upgrades have some method to deal with speculative processing, and I believe, that is only an issue with G3 processors, not with G4 processors, but I may be mistaken.
In any event, the speculative processing issue is dealt with in software/firmware by the upgrade vendors and it doesn't cost much performance. If you simply must compulsively have that last percentage or two of performance, then you need a Kansas machine (although tests indicate memory throughput may be slower) or you can replace the ROM chips on a 9500/9600 board with Kansas ROM chips which gives the speculative processing fix.
Use 8 Mbit 44 pin PSOP Flash chips which are rated at 90 ns or faster for the ROM replacements. They were/are available from a variety of manufacturers. The main issue is that some of them have a Reset pin which must be tied high for proper operation (run a little wire from 5V to the pin).
The other main issue is getting a 44 pin PSOP adapter for a chip programmer so that you can program the Kansas ROM contents onto the Flash chips...
Alternatively, the Flash/ROM chips can be installed on a ROM DIMM, but few people have the necessary circuit board available (the ROM board from a Power Computing machine can be adapted).