Flying Oslo to Beijing (3 days), then Shanghai (5 days, so 8 total), then HK? Too long to qualify?

Tami, your travel doesn't qualify for the free transit in Beijing and Shanghai. You need a tourist L type for that.

Thank you. If I am presenting a conference paper, do you think it is okay to apply for a tourist L type? Or would you recommend applying for a business or F 'non-business visit' type.

What is the most reliable and least costly service to expedite such a visa? Thanks again!

You can ask the conference to issue an invitation letter to you and then apply for a tourist L type to attend the conference. There is no need to apply for an M or F type then.
You can choose the rush service which takes one working days to process the application. It costs USD170 per person.