Standard combat spells step through five tiers — Strike, Bolt, Blast, Wave and Surge — each a real jump in base damage over the one below, so the spell you can cast keeps pace with your Magic level. Casting speed comes from the staff you hold, which is why a faster staff is an upgrade even when its bonuses match.
Powered staves are the other path: they need no runes and scale their base hit with your Magic level instead of using a spell. They are tiered, so a better staff hits harder at the same level — the Duskmare Staff, then the Trident of Venom, the Sanguine Staff, and the Shadow of Tumaken at the top, which triples your worn magic damage.
Worn magic damage % multiplies whatever you cast. Melee and Ranged have the same lever: prestige gear like the Amulet of Torment, Ferocious Gloves and the Grondar set carries a melee damage percentage that multiplies your max hit on every swing, specials included.