You usually get better performance with CF cards as they work natively on the PATA bus. IDE to SD brings in another protocol translation layer which can limit performance. Not sure if that is the problem though.

In order to get higher speeds you need to configure the IDE controller to use higher PIO speeds. This is usually done by jumpers on the motherboard or by a driver. If you have no such configuration most likely you are using a conservative setting like PIO0 which limits the performance.

Paar:
I've noticed the same thing when tested different VLB I/O cards. But I didn't have the motivation to do further investigation (jumpers, other motherboard, CF card or adapter...). Even ISA I/O cards can manage up to 2000KB/s transfer speed.

As there are no jumpers on the motherboard for this (according this link) I will probably have to use some driver, if I find any. Or I could try the DOS version of PowerIDE utility. Hopefully I'll make it work.

Yes. This is an early IDE controller. So drivers won't be talking about PIO/DMA modes. Most likely you'll be able to change active/recovery clock cycles.

Here is the spec. So I believe some tools for programming these registers must exist:

http://www.ryston.cz/petr/vlb/adi2.html

Depending on your BIOS version you might also try to update your BIOS or try to reveal hidden settings that would allow you to set IDE controller registers

I have contacted a member of VCFED forum who claims to have proper drivers. And I will try the PowerIDE app, it's worth a try. I will share my results here. I hope I will be able to bring the board to it's full potential.

Success! After some digging on the internet I've managed to secure DOS/Win3.1 drivers for the controller. Installed the DOS one (which is one *.SYS file) and after that the reading speeds increased dramaticaly. I think the only thing that limits the SD card is an old IDE standard with max 8 MB/s transfer rate. Thank you mpe for a tip, it really helped.

I'm including the driver for anybody who would find it useful.