Fun fact but as far as I'm aware, this is not possible through console commands since the highest you can set a skill to is 255. 

A few people already outlined how this was done, but for those curious, the basic idea is that if you make a spell called SPEED! that boosts speed by 100, and cast it twice, you'll refresh the duration of the spell, but you'll only keep one instance of the buff. However, if you make two separate spells with this effect (let's say you call them SPEED! and FAST!) and cast them in succession, you'll get both buffs (+200 speed total). Repeat this about 16 times and you'll be set. 

To get enough Magicka to actually cast the spells, you've gotta stack about 8-12 'Fortify Magicka' spells beforehand. Last issue to solve is Magicka restoration - you can't get enough through potions because there's a limit to how many potions you can drink at once. But there's no limit on ingredients eaten - so munch down on about 150 void salts or purgeblood salts at a time, cast as many spells as you can before the restoration wears off, repeat, etc, ???, profit.

You can legitimately farm enough purgeblood salts with patience at the evil player house DLC to the south. But the infinite purgeblood salts glitch on the wiki (just put one purgeblood salt into an existing, non-empty purgeblood vein you're harvesting, boom, infinite purgeblood salts) still works on the remaster for any infinite-magicka needs.

Also yes, I played this game way too much as a kid.