Sometimes it's 100KB/s and other times it's 900KB/s. Never got as high
as 1500KB/s though.
I did do one more experiment -- I took easymint aranym image (gcc 2.95, some old kernel and mintlib) and compiled freemint kernel + drivers from scratch. Luckily, your fixes works OK (i.e. fast) for all my tests. As soon as I replaced inet4.xdd and/or ethernat.xif with gcc4 version, some very visible performance losses appeared... Try the the same and I'm sure you'll get 1.5 MB/s as well. (of course, your ftp server must be reliable). Btw, try it with direct cable connection, as evil pointed out at ct60 bbs, every connection trough gateway is much slower than direct one in mintnet.
So it seems we're going to be stuck with old 2.95 for some time yet...