It's simply not natural to be doing over 100 attacks per second with over 1000 speed. Focus on upgrading your El's Mercy first. That's where most of your damage output and attack speed increases are going to be coming from. If you're ever unsure of what to upgrade, upgrade El's Mercy. Get Paranoia to instant cast, Clemency to 100% healing, and focus Love, Umbra, Perfection, and Predation. If you feel you've upgraded those enough, focus on Giant, Panic, Guidance, and Insensitivity. You can use this build to unlock Bismuth. I regularly get over 1k speed lasting far longer than 3 seconds with this. I recommend activating the Marsh of Destiny Lucid Dream to get Dream Dust faster. I also Deja Vu the Clemency since I have the hardest time finding it in my runs.