Could you let me know how determined that your SanDisk Ultra 50 mb/s CF supports multi-sector transfers? If possible, could you provide a screenshot? Not to be overly particular, but time and human memory can have surprising results.
To match my tests, just grab a Promise Ultra100 TX2 and plug in a relatively fast CF card to serve as the host OS. Then run the same tests you just ran copying over these large files with a stop-watch.
I think I used a Maxtor DiamondMax 10 UDMA133 platter drive. I used a Sandisk Extreme Pro UDMA7 160 MB/s CF card in the Secondary IDE port. I am wanting to check the read/write speed of this CF card on the Secondary IDE port. Using something like the Promise Ultra100, which is an order of magnitude faster, will put the bottleneck onto the MB's IDE port.
Note that if you try to put the CF in the Primary IDE port, the MB will insist on booting from the Primary port. The MB lets PCI expansion cards boot to their HDDs only if the CF card is in the secondary IDE port on the MB. Unfortunately, the BIOS doesn't have a feature to select the boot source, other than A: or C:, so this is the workaround I use. NT4 is able to see the CF card's full 32 GB. Alternately, you can use the CF card in the Primary IDE port if the target OS is located there. As noted above, I would need to get another 8 GB CF card to do that.
I haven't started using the XTIDE BIOS, but if you understand what I'm trying to accomplish, then there isn't really an option to continue using a PCI hard drive controller expansion card. I am currently using a Promise Ultra100 card, but am wanting to give it up for a second Voodoo2 card in the system. It is a big sacrifice and I want to ensure a CF card or the Maxtor DiamondMax 10 aren't too sluggish on the MB's built-in IDE controller. If it bogs the whole system down, then the trade-off isn't worth it. However, the BIOS only sees 8 GB and I will need to use the XTIDE BIOS, e.g. on a 3Com network card, to workaround this limitation.