First we visit AnandTech, they conclude the Radeon HD 5770 is slower than the Radeon HD 4870 1GB or GeForce GTX 260 but that this new 40nm part runs cooler and is less noisy. Performance-wise it's not really a great deal at $160 because this card is 14 percent more expensive than the Radeon HD 4870 while delivering 10 percent less performance. The Radeon HD 5750 on the other hand comes close to the performance of the Radeon HD 4850, while carrying the same price tag.
Next is a review from HardOCP, they gave both cards a gold award and write the Radeon HD 5750 provides incredible gaming value.
And to end our brief performance overview, we take a quick look at what Hexus has to say. They conclude it's a bit worrying that the Radeon HD 5700 don't beat older cards which now come in at the same (or lower) price point, mainly because there's too little competition in the graphics market today. Both cards will offer good value, especially as prices begin to settle down, but they're hard to recommend to anyone that already has a Radeon HD 48x0 or GeForce GTX series graphics cards.