This is the build I used for grinding Platinum.
Hover over cards for details, click for permalink
7t6 7t6 7t6 7t6 7t6 7t6 7t9 7t9 7ta 7ta 7td 7td 7um 7um 7um 7um 7um 7um 7um 7um 7um 7um 7um 808 80i 80i 80i 80i 80i 81q 8pu
Depending on the day, I think I got somewhere between a 40-70% winrate. My longest streak was 9 wins in a row, but you have to take the good with the bad - I also remember loss streaks of 4-5.
The build is pretty close to yours - 3 Steals are probably also viable, but 2 Vampires and 2 Eclipses seems to be ideal to me. Both are important cards, and you definitely want to draw them consistently, but not until the late game - you don't want them clogging your hand early on.
You can go even harder on the upgraded Aether quanta for even faster Fractals, but you run the risk of not drawing enough Darkness quanta.
Hover over cards for details, click for permalink
7t6 7t6 7t6 7t6 7t6 7t6 7t9 7t9 7ta 7ta 7td 7td 7um 7um 7um 7um 7um 7um 7um 7um 7um 808 808 80i 80i 80i 80i 80i 81q 81q 8pu
I think 4 Fractals is, mathematically, the best option for this deck, since most Devtal/Pestal games are typically won as soon as you play your second (one on Pests, one on Vampires) - that said, I've played too many games, casually and competitively, where I haven't drawn a single copy in the top half of my deck, so I also prefer running 5. You can experiment with both and find out what works best for you - replace the 5th Fractal with another Dark Pendulum if you go that way.