In general turbo dial up is a process where text and some graphic files are compressed to make them load faster. Things such as streaming audio, video and games will be no faster than regular dial up. As far as speeds go, turbo dial up is nowhere near as good as dsl or cable.
Here is a statement from TalkAmerica.net: Talk America's Turbo ISP product uses server-side compression and cache technology to reduce the size of pages before they reach your computer and decrease the time it takes to view websites.
The software accelerates HTML, Javascript, JPEG, GIFS, BMPS, text, and e-mail. It does not accelerate streaming media, secure websites, file attachments, digital music, or digital photos.
Turbo 5X makes it seem like you're surfing at up to 5x the speed of a typical 56k connection. This is the same type of software that other large competitors such as NetZero and Earthlink use.