If you have to guess, go with an 80 wire ribbon cable of shortest workable length. Now, folks, it is possible to find an 80 wire cable that is TOO cheap, so do look for a name brand. The cable matters.
If you want a better guess, go with an 80 wire ribbon cable that has reinforced ends (an extra-thick ridge across the connector and some sort of handle for disconnecting without pulling on the cable itself), and make it of shortest workable length. This is similar to the cable included with retail units. Some evidence of extra effort going into the manufacture of the cable is a good sign.
If you want really bad performance, take a shot in the dark on a thin round cable.
If you want slightly below optimal performance, go with an obsolete 40 wire ribbon cable. That's like the cable mistakenly packaged into the I/O Magic boxes. LOL!!
Still, this is much better than a thin round cable.
Some large, thick round cables have enough sheilding to conform to the 80 wire ata 133 spec of one sheild (or reverse) per data line. These are good, however a low-noise, quality power supply becomes more important when using rounded cables (because now the 12v power lead that operates the interface and light is firmly pressed onto the data lines).
Check reviews to find out which round cables are "good" because most of them totally violate IDE specs.
If you have the DVD Writer as the only IDE component in an otherwise SATA system, then you should consider using a converter block. Abit makes a good converter block. Thes plug into the back of the drive and then you can hook up the drive with SATA. After that, disabling the onboard IDE system (Bios setting to disable) will increase your overall system speed by freeing up a considerable amount of computer resources (2 irq's, 2 dma, 4 memory addresses, and numerous software drivers).
Above all, use short, heavy, name brand, and well shielded cables--for everything.
This reminds me of the thin Chinese electric blanket I had when I was 3 years old, and one night. . .ZAP!! That's another story.