Minimal internet speed for multiplayer?

[LilStarla]

I've been playing with a friend and lately she's run into a 'slow-motion' issue. She sent me a video of her screen and sure enough the game was running in literal slow motion. She said it doesn't happen at all if she plays offline in single player, but whenever we play multiplayer, it starts to happen again. But it also isn't constant. She says it comes and goes sporadically. One moment it runs fine, the next she's chugging around in slow-mo.

I had her run an internet speed test at speedtest.net and she had around 5mbp/s DOWN and 0.6mbp/s UP. To me, that UP speed is incredibly slow and I personally believe that is her problem. But it hasn't always existed, so I'm pondering the possibility that her internet became slower somehow...

What we have tried: general clean up and maintenance of her PC. Everything is fine. It runs a lightly modded Skyrim like a charm. Turning off multi-core lighting, playing around with frame-skip. Making sure her video card is up to date, setting vsync, triple buffering to ON. Disabling mods (only Tremor, tModLoader).

So... with all that said I guess I can ask my stupid question... just what are the recommended down and up speeds to play the game in multiplayer? And if her speed is sufficient, what all could cause the slow motion?

 

[Casu]

The only reason I can think of is having frame skip off. The only issue is that turning frame skip on will just replace the slow motion with low frame rate.

 

[LilStarla]

I probably shouldn't have mentioned that since her PC runs the game well regardless of frame skip settings as long as she is offline and playing by herself. It's only during multiplayer she experiences the problem.

 

[Casu]

On my old PC my frame rate would be fine but in multiplayer it would be lower so how good is her PC?

 

[LilStarla]

I'm not sure about her CPU and chipset, but I know the GPU is an nVidia GT640 1GB, system RAM 8GB. And like I said the issue has only recently come up, and it can run a lightly modded Skyrim on max settings (@1920x1080) with no such problems... except for the common Skyrim CTD...