Gordon,
I think you've answered your own questions.
The problem is usually the provider's server and the content.
Pop-ups, scripts and all the other crap running on web pages dramatically slows performance on what you want to actually see.
Some browsers cope with this better than others too.
I have found Google Chrome to handle this the best so far, but we are all at the mercy of the web server...... eg: the slowest link in the chain.
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