write in terminal emulator, not also (...):
(Write file 64MB (8k * 8192) bigger file is better)
busybox dd if=/dev/zero of=/data/out.img bs=8000 count=8192
busybox dd of=/dev/null if=/data/out.img bs=8000
(to Remove out.img)
If you don't have int2sd and let /data the phone writes in nand.
If you change / data in /sdcard or /sd-ext you can test your sd-card speed.
Report in this thread your results.
If the test is positive we can ask to our developer to try to include this NativeSD script in roms.
Edit: use androbench from market and try both /data and /system.
(I read this information from N1 jb evervolv thread)