>In my famous naivity I tried to use an old 486 @ 50 MHZ as my DSL router.
>Running the rp-pppoe pkg from pkgsrc this results in abysmal performance
>(limiting download rate to something between 10 and 20 kByte/s instead of
>the expected ~80kByte/s for my connection).

Dumb question...  PPPeE implies that your DSL modem provides ethernet
yes?  What does the PPP bit get you?  

When my DSL link was working ;-( I was using a sparc classic (about equiv 
to your 486@50 :-) with two ethernet interfaces as router and doing 
ipf and ipnat was easily getting the full 400k throughput expected. 
(400/400 SDSL).

--sjg