From Newsgroup: comp.sys.ibm.ps2.hardware

https://archive.org/details/bitsavers_ElectronicignV39N0519910314_84303651/page/n75/mode/1up

A performance boost of up to 290% for systems currently
using the full 32-bit 80386DX microprocessor from
Intel Corp. is now possible by substituting the more
powerful i486 processor. However, rather than redesign
the entire system motherboard to use a new chip set and go
through the component requalification process, existing
i386-based systems can be modified with the addition of
about seven active components to accept the i486 processor
and run in the non-burst mode. The cost of the modification
is about $30, not counting the cost of the new CPU.
Benchmark performance comparisons between
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