Intel 80287 coprocessors
The 80287, internally, is the same math chip as the 8087, although the pins used to plug them into the motherboard are different. Both the 80287 and the 8087 operate as though they were identical. In most systems, the 80286 internally divides the system clock by two to derive the processor clock. The 80287 internally divides the system-clock frequency by three. For this reason, most AT-type computers run the 80287 at one-third the system clock rate, which also is two-thirds the clock speed of the 80286.
Because the 286 and 287 chips are asynchronous, the interface between the 286 and 287 chips is not as efficient as with the 8088 and 8087. In summary, the 80287 and the 8087 chips perform about the same at equal clock rates. The original 80287 is not better than the 8087 in any real way - unlike the 80286, which is superior to the 8086 and 8088. In most AT systems, the performance gain that you realize by adding the coprocessor is much less substantial than the same type of upgrade for PC or XT-type systems or for the 80386.
Source: Upgrading and Repairing PCs (13th Edition) by Scott Mueller.