I have a similar problem - but mine constantly buffers (every 5-10 seconds). SQ is fine but bitrate is 5-600kbs. Streaming on Windows 7 PC (FireFox) also fine, at HQ 1200-1300kbs, on the same network, same period of time. I have 2 dots for SQ, 4 dots for HQ. Have tried all the suggestions. There are others who have reported this problem as far back as June 2011 but there is no fix supplied to date.
I have tried this on an iPad 1 and 2. iOS 5.0.1
Upload speed from home network is 1700kbs, download here is 15Mb. Netflix works fine on HQ on the iPad, as does YouTube HQ.
Slingbox website reported internet viewing setup is complete (has been for ages). I am using a Slingbox SOLO (Slingbox Software Version: 2.1.250)
I don't think there is anything amiss with the network or Slingbox setup, otherwise the FireFox viewing would also be as inferior.