I also use ppp, on current from September with a USR sportster 33.6
external, dialing the same kind of modem on another NetBSD machine.
Throughput/speed seems to be fine, limited by the modem.

I do have another problem, which is that when the line goes down (due
to modem hangup - this is a nailed-up connection), pppd notes this,
unconfigures the interface, and then hangs in a wedged state where it
doesn't exit, or worse, do the redial commanded by persist.
But I think this is unrelated to performance issues.

Try running tcpdump and analyzing what is going on.  There may well be
other issues.  pkgsrc/graphics/xplot is helpful for analyzing tcp
performance, but that probably isn't necessary.


-- 
        Greg Troxel <gdt@ir.bbn.com>