I'm making my own PCB connectors using the "multicomp" range of crimp connectors available from farnell (ex. http://uk.farnell.com/multicomp/2226a-04/crimp-housing-1-row-4-way/dp/1593508 with terminals at http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1593529&MER=baynote-1593529-pr), but while I'm able to get a good DC connection and solid mechanical connection (the terminals don't pull off easily), the AC performance of the resulting cables leaves a lot to be desired; I don't have a lot of test equipment here but with a simple home-made test (wiring them up to an FPGA development board and looping back to the same board and seeing how fast a signal I can send through them and receive it reliably), it appears I can only get up to about 500KHz before I lose the signal. I'd have expected to be able to do better than that, as I've seen this type of connector used for signals I assume must be higher frequency than that (e.g. USB2).
Any ideas what I can do to improve the performance beyond this? What kind of frequency should I be able to usefully achieve with this type of connector?
EDIT: I'm putting them onto CAT6 cable. Is this a suitable cable or do I need something heavier?