Have you thought about using a download manager?
"Download acceleration, also known as multipart download, is a term for the method employed by software such as download managers to download a single file by splitting it in segments and using several simultaneous connections to download these segments from a single server." (Wikipedia)
I downloaded The Witcher 2, which really is a huge file (over 16 GB), so large that they have already split it in segments of 2 GB each that you can download separately with your browser, but using GOG's downloader, I had the whole thing in hours with a dsl speed of about 10 Mbps. The default on the GOG downloader is 4 simultaneous connections, as I recall. So, I know they work.
Unfortunately, I haven't used any other download manager in so long I can't recommend one that's fast, free, doesn't add things to your computer you don't want and is safe, but maybe someone else can.
"Best not to think about it. I don't want to fall to bits 'cos of excess existential thought."