The 350 and 500 require a minimum of 2.6 Mbps to stream in HD. The PRO-HD can do 720p down to 1.2 Mbps, but will drop lots of frames during fast motion when running at your 2 Mbps speed.
If your contracted upload speed is much higher than what a speedtest shows, there may be a problem with your modem, router or line that can be fixed.
If you're willing to pay for it, your ISP (or a competing ISP) may offer higher upload speeds.
Otherwise, you'll have to settle for a 480p picture.