I own both devices and it's a great question.  The One X and Sense 4 are very close to the 4s and iOS IMOP in feel and how fluid the OS feels.  ICS has made a lot of strides and is much smoother then GB, but it's not iOS smooth yet.  However, having said that coming from a 4S to the One X I don't think you will notice the difference at all.  I have not had any crashes or stutters etc and scrolling from screen to screen is as smooth as iOS even with widgets on which is something I couldn't say about GB.  The processor in One X is quick and from other bench marks that have been posted very quick even beating the Tegra 3 in some cases.  I would rather have LTE over the Tegra 3.