[Hampshire] APIC, interrupts and wired NIC

I'm installing a Debian distro on a Fujitsu LifeBook which has a built
in 10/100 NIC using the e100 module. All seems well except that I
can't get more than about 50k throughput. When I investigated, the
'overruns' count in ifconfig was steadily mounting which indicates the
machine wasn't responding quickly enough to incoming packets on the
LAN. With the CPU at around 3% this seemed odd, so I looked at the
IRQ's and found that eth0 was sharing /proc/irq/9 with ACPI. I
rebooted with acpi=off and was able to get the normal 7-800k
throughput.

I don't really want to disable acpi but equally I'd rather not lose
the NIC speed. I've tried combinations of acpi=noirq, pci=routeirq,
acpi_irq_pci and even netdev=10 but nothing seems to shake ACPI off
sharing irq 9 with eth0.

Anything else I could try?

How bad is it to disable ACPI?

TIA, Peter