The Custom V is directional twin (d-shape, twin flex). The T-Rice is true twin through-and-through.
The Custom is about medium flex. The T-rice is pretty solidly a medium-firm.
The T-rice has considerably better pop than the Custom.
The Custom rides loose as fuck thanks to an exaggerated "V" rocker. The T-rice is much more stable and doesn't feel like you're "balancing on a fruit bowl" (to quote BA). There is no comparison between these boards in this department.
The T-rice rides damper than the Custom and has better edgehold; I don't know what Burton's doing with Frostbite but honestly it's barely noticeable compared to Mervin's MTX or Arbor's Griptech.
If you've ridden these two boards and still think they're the "same tech" then you should be automatically disqualified from talking about snowboards to anyone, anywhere, ever.
ummm, it's a custom flying v, dude, not v-rocker