Apply the qemu-slirp-performance.patch from Kenneth Duda available here: <http://lists.nongnu.org/archive/html/qemu-devel/2006-04/msg00245.html> This does improve slirp performance a lot, especially in FTP passive mode transfers. i.e. now, they are equally as fast as non passive mode. I get approx. 800 KB/sec in B2 and 500 KB/sec in SheepShaver (over a DSL line). In native env, the max download data rate from my ISP is around 950 KB/sec.
slirp user mode network emulation code from qemu
This form allows you to request diffs between any two revisions of this file. For each of the two "sides" of the diff, select a symbolic revision name using the selection box, or choose 'Use Text Field' and enter a numeric revision.