Nothing wrong with winmodems.
I've been using a USR ISA, and now a 3Com ISA, hardware modem for years. Normal connection at 49,333. Been sticking in those $5 PCI winmodems in others PC's for years as well. Normal connection 46,666, which is what my external Best Data hardware modem gets on a good day. Big deal, and you can't even tell the difference. However, if it's using the Lucent chipset, newer drivers are a must.
Lucent Win Modem drivers and firmware..
10-15% CPU utilization? I don't think so. Back in the early days, when CPU's were running at 166mhz, perhaps that was true, which would mean they used 16-25mhz of that 166mhz cpu. 16-25mhz of todays 600 to 1Ghz cpu's works out to be around 1 to 4%, and isn't even noticable. It's much, much less of a hit than a normal sound card takes away.
You want speed? Team 2 or more 56k modems together, using some of the great software now available. I'm using Midpoint Gold to get close to 100k connections, using 2 netzero accounts.