I've always had poorer response from Netflix using my computer than when I use Warner Archive streaming. Today, my usenet server offered free VPN service included at no extra charge. VPN is a virtual private network, meaning, you connect securely to a local server and from that point on, your info is untraceable. If you download material or stream, it all goes through the VPN. To your ISP it looks like everything you are downloading is coming from your virtual private network, not the IP addresses of the various sites you visit.
This effectively makes Netflix streaming invisible to your ISP. If you connect directly to Netflix, they see the Netflix IP on the other end and throttle the connection. But going through the VPN, it goes full speed.
Strangely, using my Roku 3 box, Netflix HD locks in quickly and the stream is rock solid. I suspect the Roku box is going through something that hides the Netflix IP from my ISP, but my Mac using Silverlight gets flagged by my ISP (Verizon) and throttled. No longer.
Anyone who is getting poor Netflix performance, yet has a super strong internet connection might want to look into a VPN account. The benefits are worth the trouble... super safe and secure data transmission, no hacking, no cyber spying, and great Netflix streaming. The service I am using logs you in automatically at start up and has no data caps or limits. You can even use it on the road in foreign countries to bypass internet region blocks and have secure private connections at shared public networks at coffee shops, etc.