If you have all 6 star artifacts with at least 1 roll in speed plus 6 star speed boots plus 6 star banner with also 1 roll in speed. Then add some glyphs to them, and you can have at least a 200 speed champion. 

You can get to 260+ by farming dragon lots and rolling gear repeatedly for double/treble speed

I think whales buy the speed kits - which plarium are more than happy to sell of course- that way they get above 300 speed

I am 252 speed (before aura) and i dont even bother to try fighting speed teams as i lose every time.

Like was mentioned. Boots with Primary SPEED stat and 5 or 6 star artifact will get you 45 speed from that  single artifact

Your champion likely has already 95ish speed without anything

If you equip 2 artifacts from speed aura set that will give you another 10 to 15 speed

Now if your other artifacts (Helmet/shield/gloves/chest/weapon) also have a sub stat of speed on those artifacts each piece could get you 5 to 10 on average more speed

then enchant those artifacts with speed glyphs for another 4-5 pts each

add it all up and you are well over 200 speed. But yes this takes tinkering with gear to get it and if you do not have enough gear with speed you will need to farm it as already stated

Hope this helps and goodluck :)

p.s I just used average  numbers for this example but the results will be similar

what do you mean ** rolling gear repeatedly for double/triple speed ** ? 

What Dungeons Drops 6 star ,, OH YA 20s ,,, 

Good luck till you get the Right team set up and Pull the Right Heros

Dungeons at stage 13 already drop 6 star artifacts

You collect gear with speed substats and roll it (level it) hoping it will increase the speed substat multiple times. It requires either buying speed packs from plarium, or farming till your eyes bleed, and then farming more.

Masteries, Minotaur Scrolls, lvl 6 artifacts maxed out with the help of glyphs. Select artifacts with one of the substats as speed. that should do it