SAE90 final drive oil?

Would it be ok to put SAE80 gear oil in my C800? I have an almost full bottle which i got for my Virago 535 which was also shaft drive.
Would SAE80 be much different to SAE90? 
Thanks

I would not think there would be a problem mate! 90 is a bit thicker but not much & seeing as it was intended for another shaft drive bike then I'd use it myself anyway.

I have just replaced my oil with some shell transmission oil and I think it said it was suitable for use as SAE80/90, from what I have read, I honestly do not think it will make any difference in the UK.

Use it, it'll be fine.

You will have no problems using it 

It was recommended for my GS 850 years ago, use it, it's fine.

Thats good then, didnt want to blow a tenner on a slightly different grade.
Is it neccesary to ride the bike first to warm up the oil in it or can i go ahead and change it cold?

Just empty it and refill