I don't think anyone's really figured out a good balance for the AI. I've found that by giving the AI more science yield percentage, it doesn't really help them fend off an early war, but if left alone (or if they gobble up their neighbors) they tend to snowball out of control mid-game. There are so many factors that affect how strong the bonuses really are. For example, if you're playing a duel sized map, you could probably give the AI 500% boosts and still win without much effort by taking them out early. Whereas, on a huge map, especially with many players, the one AI in the corner may have a ridiculous lead on everyone else even without a massive percent boost, especially if they gobbled up their neighbors and snowballed.
If by 150, you mean Value, that's substantial. That means the AI gets an additional +150% science (250% total). For reference, on vanilla Deity, the AI gets +100% (200%) science.
I've personally liked the Smoother Difficulty mods, which take away the starting tech boosts and settlers for high difficulty AI, but greatly increases their percentage yield bonuses. This makes it more feasible to get a religion on higher difficulties (as opposed to necessitating starting next to a Natural Wonder for the Astronomy eureka just to be able to even get a chance at getting Great Prophet before they're all taken), as well as making it so that early game, if you happened to start next to an AI, they won't immediately declare surprise war with their 4 warriors vs. your 1. At the same time, it compensates the AI by giving them higher percentage yields to roughly do just as well mid and late-game. Like I said though, it's not perfect, and I've run into many similar issues as above, but I've found it much more enjoyable than vanilla difficulties where the AI is insanely overpowered early-game, but as long as you survive into the Industrial Era, it's almost impossible not to win.
I hope you have fun experimenting and end up finding a good balance that makes the game more fun!