865PE Versus 875P
On paper, the Intel 875P chipset (code-named Canterwood) is designed to be a high-end version of the 865PE chipset. It has the same features as the 865PE, plus it adds support for ECC (error-correcting code) memory and features what Intel refers to as Performance Acceleration Technology (PAT), which bypasses normal steps in the memory-access portion of the chipset.
However, in practice, the 865PE and 875P chipset cores start out in the same production line. In a time-honored Intel tradition, the fastest cores wind up in the 875P, complete with ECC support, while the rest are shunted over to the 865PE production line (the 875Ps MCP chip has extra connections to support the additional signals needed for ECC memory). Some motherboard vendors, most notably Asus and Abit, have figured out how to enable the bypass function with the 865PE chipset, although they are prohibited from calling it the faster PAT (Performance Acceleration Technology).
In tests, there is little if any difference in performance between the best 865-based and 875-based motherboards. If you need the extra security of ECC memory, the 875P provides it, but otherwise, the 865PE is the best bang for the buck.