I have 100/100 up and down, and I barely push any more than 3MB/s when uploading. and in that time the client is easting all cores alive. I appreciate that it may not be the ISP. but the client does seem to end up being a major bottle neck.

I moved to Linux a few months back, and was going to basically cancel my Backblaze sub when I got around to it since you have no interset in making a Linux client. Maybe B2 can act as a solution to this at a price penalty.