ip fast forward on 6.2

[J.D. Bronson]

Is it proper to enable 'ip fastforwarding' on 6.2 when running pf ?
I am attached to a cable modem (10MB speed) and only use DHCP.

I have a 6.2 machine thats being used as a router and of course ip 
forwarding is enabled...but when I try to enable ip fastfowarding, I 
see throughput drop or surge up/down whereas without this enabled, 
throughput is higher and more consistent.

I have to use both or forwarding of packets doesnt work.

Anyone have any comments on this good/bad?

-JD