I like the question
First, there is some truth in the specified claims about Allendale Core processors containing 4096KB L2 ECC cache.
Allendale cores, if manufactured to be Allendale cores themselves, will not contain 4096KB L2 cache (including 2MB disabled). They will contain the 2048KB L2 cache that they have been designed with, and the additional 2MB L2 will not be present on the physical chip.
If a Core 2 Duo E6600 (or greater) is unable to operate at the required clock frequency the chip itself can be reduced the E6300/E6400 part, and therefore Intel will disable half the 4MB L2 cache.
Please be aware that if this is the case you will have the ability, depending on your skill, of reactivating the additional half of the Main L2 Cache Array.
If a Core 2 Duo E6600 (or greater) is unable to correctly address (or contains a manufacturing fault) the 4096KB L2 cache, then half of this system will be disabled. Obviously you can attempt to reactivate the additional cache, but it will not obviously work.
The choice is yours, you have a fairly high risk of doing physical damage to the internal components of the processor if you tamper with it to this engineering level.