| Got to disagree with that mate the thicker the oil the harder the pump is going to have to work to get it up there and the more frictional resistance will be created.
I once had to drain some virtually new 20/50 from a bike and left it in an open pan over night in the shed in winter, when I went back to it next morning it was like treacle if that had been in your bike I think it would have taken even longer than 90 seconds to get up there.
You could possibly prove this, a post I have recently read was about how hard it is to start an SPS when cold in winter, try a lower grade oil and I bet it starts easier. | 
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