I wonder what you did differently. Many others who have tried this couldn't get it to work. The 5770/5870 drivers were not included in SL until 10.6.4 and later.
1) Benchmarks show ML is faster than SL for CPU, GPU, and disk writing. It is about the same for memory access and desk reading. I haven't found any area where it is slower. Also, the graphics drivers are unquestionably superior in ML as that is where all of the updates are going. SL graphics drivers are getting to be ancient.
2) ML is not "integrated" with iOS. I feel like a lot of people have complained about this without being able to explain what they mean. Yes, there is a Messages application, Game Center Application, and Notification Center application and that all sounds very iOS-like. But these are applications. You can just... you know... not open them? Okay, there are also some applications that have been updated so they can sync information with your mobile device, such as Notes. But you don't have to enable synching; it is optional. So... don't enable it? By default it's not enabled. To call this "integration" is very misleading.
I really think if you don't need Rosetta then you should just move on to ML. Look, I'm a fellow SL lover who hung on as long as possible. I completely skipped Lion and I only begrudgingly upgraded to ML. I have no regrets. It is demonstrably faster and the "iOS integration" is overblown nonsense.
But hey, do whatever you want. It's just my point of view.