Rooting is not the straightforward Way to Boost speed of your phone but for sure you can claim some serious phone memory alongwith cleaning up bloatwares that comes pre installed with phone which might help to improve performance.
Consider Sam's Guide In this section for rooting your phone.
Links provided by Techfreak just above.
The best I can recommend is, MiniCM7 2.1.9. by nAa. It is basically CM7 with with nAa's editing. It is the best Custom ROM out there for X8 ( or even for E10, U20i).
I ould also suggest u to get the custom kernel by nAa. It has quite a number of advantages over the stock kernel.
There are no FC s or slow ups in the mobile. The speed will be very good. (Though in new condition... sony's stock UI is also very snappy). what is doesnt improve a lot is its battery life(especially if you use internet all the time). If you are ok with the current battery back up... you would be happier with this one.
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