It could be that some other factors as type of internet connections we use, and combination of some other security related programs are dealing with this issue...
Also, having hardware router/firewall affects the speed. I'm running my D-Link DI-604 without any problems... never ever had any problem with internet connection. I'm not saying some other, different types of routers and different router/firewall configurations can not cause some additional problems. All those factors should be checked, so Alwil can collect more useful information and work on this issue...
People, post your configurations, all other security programs installed on your system, especially those which runs in background (resident tasks), most important hardware components you have (like routers/firewalls) etc...
Then eventually, Alwil will see better what's causing those problems on certain systems...
Thanks !