For the best viewing results Roku's recommend a minimum of 1.5 Mbps for standard definition and 3.0 Mbps for HD content.
Here's one more way to test your network speed....
It all depends what server you choose to run the test with.
I am in Oklahoma (ISP up to 10.0 mbps...never got anywhere near that, Suddenlink says that is what they supply and it's not their fault that I don't get that speed. They also said sites like Speakeasy, Speedtest etc are worhthless as they don't really show what speed the ISP is really giving you), if I choose Dallas I get about 4.5mbps and if I choose Chicago I get 7.0mbps
I do wonder what server you should use?
Where is the Netfix or Roku stream originating?
speedtest.net is dead on for me, reflecting both what I pay for and what I get in normal operation.
Accuracy will depend on a number of factors, like distance to the test server, ISP congestion, quality of the ISPs peering, local network, computer speed, etc. Treat it as a data point, but if (as the original poster) your speedtest is under a megabit, you're probably not going to get a satisfactory experience.
Another data point is at pingtest.net:
The first of those is from a computer with a hard wire, so the latency is a little lower. But for some reason that computer can't complete the packet loss test. This test uses a java applet, and is a bit heavier and harder to get working than the flash-based speedtest. But it can get to some of the issues that can kill netflix streaming on the roku. High loss, high jitter, and high ping times can all indicate situations which the roku can't handle very well, even if another device on the network can still pull down decent speed test results.