@ trimis:-
Nah, you should be fine. Mixing different SATA interfaces is very like mixing different speed RAM sticks; they'll simply throttle back to the slower interface.
Illustration; the elderly Compaq desktop tower I'm posting this on dates from around 2004. It was built at the time when SATA was just starting to appear in the marketplace, so consequently this mobo has both SATA-1 ports
and IDE ports on the same board.
When I inherited it from my sister about 5 years ago, it still had the original WD Caviar 'Black' 160 GB IDE/PATA drive it came with originally. A couple of years ago, the drive was beginning to show signs of finally packing up (at 14 yrs old, it'd had a good run!), so I replaced it with another WD; this time, a 500 GB WD Caviar 'Blue'. By this time, of course, you could only get SATA-3 drives.....but I plugged it into one of the two SATA-1 ports, and it's been as good as gold to this day.
Data transfer is still double the speed of an IDE drive.....
(*shrug*)
Just my two-penn'orth, FWIW.
Mike.