Firewall Speed

[bc]

I want to run 6.1_RELEASE with Packet Filter(PF) configured as a gateway 
using 2 identical 10/100 nics, on an old 450mhz pentium with 256 meg ram 
and an 8 gig HD.

In general, should I expect any speed performance issues with internet 
access base on the processor, ram and bus speeds of the MB?
Would the PF config cause any speed performance deficiencies?

I had same setup as above but with IPF firewall and received complaints 
about surfing speed so I put them back on a Linksys router firewall.

bc