To be honest, a "custom rom" is not really going to do any of that for you. I mean, it will remove bloat... But that bloat isn't doing anything except sitting there.
I think back in the Eclair and Froyo days a custom rom like CM really helped the experience. But now - stock roms are the smoothest, bug-free roms you can run. Custom roms are more about options and customization. But I haven't been on a custom rom that I can remember that has been any faster or smoother than the firmware that came on the phone.
Just my opinion.
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@theop - thanks for the post. Have you noticed any negative impact as far as performance when using this root method? I understand that it is a kernel exploit - so I was told that it would absolutely not effect the phone performance. But I love some input from a first hand user.