A traditional speedtest won't provide the insight into the speed gains with the XT. What you are seeing is the traditional HDD @7200 rpm speed being tested not the NAAD (8 GB). There is no way to test the NAAD since it is a backside cached to the HDD. Where you will really see the gains are will be during computer startup, shutdown, app launches and frequently opened documents, photos, etc. Very much like the new fusion drive put out by Apple.
All things being equal go with the XT if the price is right.
Hope this helps.