cable is usually pretty stable. i have had a lot more erratic speeds with DSL since it spiked whenever i used the phone. i have gotten around 700kps dl sped fastest with a 1.5mbps speed cable which isn't the fastest ones. most modern cable providers let you have 3 mbps speeds.
My 1st Build: Antec SuperLANboy Case| Antec 480W Neopower| 16X Sony DVD-ROM | Nec 1.44 FDD | WD 74GB Raptor 10,000 RPM SATA HDD | Aspire Keyboard w/optical Mouse |Geil Value 1Gig| ASUS P4P800-E Delux Socket 478 | P4 3.2E 800FSB HT | eVGA GeForce 6800GT 256MB