I'll spare you the cut and paste since you probably already know how much potential winmodems have. I will say that the Ambient/Intel chipset is one of the very worst. The drivers are not bad interface-wise, but performance and line handling leave much to be desired.
The leaderboard for softmodem chipsets:
1) Lucent LT
2) Conexant HSP
3) 3Com/USR, Conexant HCF, PCTel HSP, Motorola SM56
4) Ambient/Cirrus Logic/Intel
Number 1 is often faster than the most expensive hardware modems, number 2 is only about equal to them, number 3 is slightly slower, and number 4 sucks at this point. Keep in mind that with winmodems, the drivers ARE the modem, so the situation can be reversed with a simple driver update.
Modus