No speed diffrence, you are still limited by the mechanical nature of the drive. The benefits are the cable size and length options and that most modern motherboards only have one IDE connection on them.
Actually, SATA is faster than IDE, just probably not fast enough to warrant an upgrade, unless you have the older ATA 100.
Here are some specs:
Common Buses and their Max Bandwidth
PCI 132 MB/s
AGP 8X 2,100 MB/s
PCI Express 1x 250 [500]* MB/s
PCI Express 2x 500 [1000]* MB/s
PCI Express 4x 1000 [2000]* MB/s
PCI Express 8x 2000 [4000]* MB/s
PCI Express 16x 4000 [8000]* MB/s
PCI Express 32x 8000 [16000]* MB/s
IDE (ATA100) 100 MB/s
IDE (ATA133) 133 MB/s
SATA 150 MB/s
Gigabit Ethernet 125 MB/s
IEEE1394B [Firewire] 100 MB/s
(From website:
http://www.directron.com/expressguide.html)