stefanattardo: i did what you mentioned and put the number of connections to 1
Actually, if the concurrent connections is set to 1, it will only use 1 thread to download the game installer, which should be the same as if you've been downloading through the web browser, and I think it's something like 1MB/s at least. If your line can handle higher speeds, increase the number of concurrent downloads to double or triple the speed, until you reach your line's limit.
In case 1 connection from the downloader is slower than downloading through the browser, check your antivirus/firewall to see if they are blocking either the downloader or the CDN gog is using, which I can't recall atm.
Also, more than 1 connections only work (currently) with game installers, not with patches, bonuses or mac installers.