Myles,
Setting it to 1 or 2 gives what looks like the same output. It causes coreboot to fail with the following error:
Initializing CBMEM area to 0x3fff0000 (65536 bytes) Adding CBMEM entry as no. 1 Moving GDT to 3fff0200...ok High Tables Base is 3fff0000. Copying Interrupt Routing Table to 0x000f0000... done. Adding CBMEM entry as no. 2 Copying Interrupt Routing Table to 0x3fff0400... done. PIRQ table: 176 bytes. Looking for bad PCIX MHz input get_pbus: dev is NULL!