I like the digit to. The only reason I would think about using the matrix over the digit is I could have up-shift and down-shift arrow indicators for when the system thinks you should be up-shifting or down-shifting.
For the ring I was thinking of having the led's rotate around the ring according to RPM and have it change and fade color from purple to blue to green to yellow to orange to red. When it reaches the shift threshold the entire ring will flash white.