I think it should work. These connectors seem to have relatively low capacitance.

They were used for ATA hard disks, and they were working with pretty long ribbon wire with bus speed up to 33MHz, so without that ribbon cable there should be no problem with 125MHz, especially if you are using differential signals.

Source:

Upgrading and Repairing PCs Scott Mueller

http://books.google.com/books?id=E1p2FDL7P5QC

I think it should work. These connectors seem to have relatively low capacitance.

If you are really worry about this - you may try to pass 125MHz or even faster signal from lab generator and see what is going on oscilloscope.

These connectors were used for ATA hard disks, and they were working with pretty long ribbon wire with bus speed up to 33MHz, so without that ribbon cable there should be no problem with 125MHz (or 125MHz differential signal).

Source:

Upgrading and Repairing PCs Scott Mueller

http://books.google.com/books?id=E1p2FDL7P5QC