That is because they did not update with Lenovo's 8.1 drivers

No problem. Hope this helps. 
Every computer shop can help you upgrade that. You can even do it yourself, because its easy. I mean, seriously. Just remove the battery and power cord, remove the screws at the back (9 total), and you good to go.
Haha sorry, I don't have much time nowadays. Too much work, even at home. 

Yeah extra screws, happens a lot with me before. It just because we didn't take note of every phase of disassembling. Just take picture / follow the manual carefully to get rid of this problem.
Yeah, seriously.  You can refer the before and after Furmark test. Before the repaste, my Y480 reach 93C easily in just 1-2 mins. Now, I can even ran Battlefield 4 (1920x1080, low setting) from 6pm - 12am yesterday and the maximum temp it reach was only 72C for whole 6 hours (average was 65C).

Well I kinda assume that result. Because for Y480, normally GPU temp should stay around 70-80C maximum. My friend Y480 (that bought together with mine) reach maximum of 80C, while using stock thermal paste.

Yes, just like you said, maybe the previous thermal paste used by Lenovo to my laptop is not a good one. They might even use the cheapest paste in the market. The thermal already dried up completely, and I can see they just 'taruk cincai' the paste to both CPU and GPU. 

So I conclude my Y480 reach 93C before was abnormal case. Above 90C is definitely not normal. Normal case for Y480 will reach ~80C, so if we re-apply the paste, it should down to 72-75C (5-10C difference, just like you said). I prefer MX4 also, but I think both MX4 and Freezing Point should show identical result.

Edit: I forgot, I believe the fan (for my case) also affecting the temp. Although I ran the Fan Dust Extraction app regularly, I still can see there's some dust clogged between the tiny space of the fan blades, so I vacuum all.

Happen to me to when I upgraded to 8.1. Then I went to lenovo's website and downloaded all the 8.1 drivers. No the computer works like a charm including sli.