Important Question

Depends how fast your computer speed is, what graphics you set it too etc, there is no proper answer until you test it out yourself ^^

Yeah, loading all of the blocks / water / lava, will obviously be a lower FPS compared to having no blocks, water, or lava in the sky. But like i stated before, if players have access to ground level, and the sky map, then it may make it lag a bit.

It would actually be best to make the map in the sky, this way their pcs wont have to load all those blocks back at the ground, so the answer is a no.

NO, your PC WONT lag when your in the sky.

Minecraft usually runs faster with greater FPS when higher in the sky for me. I've tested this thought on 4 different computers. So far all results are positive

It depends, if you have part of the map really low, and part of the map in the sky, then it will lag hard. Because it will load alot of chunks along the way. If you're making a sky map, make sure it is all in the sky, or people will most likely experience lag.

It depends because if minecraft is running fast on your computer then it should not lag at all, pretty much no where in your world will lag. But if your computer is pretty slow then, yes. If you want minecraft to run really fast go on to your options, then click "Video Settings" and click on "Graphics" and put it on fast. It makes your computer run faster for minecraft. Also "Clouds" turn it off because it slows down the computer and can lead to lagging. Do this only if minecraft is lagging anywhere in your world even in the sky.
I hope this helps you.

Well you can't lag in the sky because people make sky maps and a lot of people don't lag on those maps.. I flew onto sky houses and I did not lag.

So the answer is nope. You don't lag in the sky.
I would not worry about it.

- goobersfussfuss

Nobody will lag, so don't worry about that. If they lag, it may be their video card. Tell them to fix their settings. Hope I helped.

Ah.. I run Minecraft on a good 150 FPS. It all depends on the computer you are running on.

Im making a map in the sky and i don't want people to lag the whole map

I don't.. Why?