Just came back from a short but intense ride. Got to test out my Boardwalk fully, especially the shifters and the wheels. No problem with the wheels now, after I changed the tubes and put extra rim tape. Hopefully it holds with no further problems.
Comparing XT and X9 shifters: Conclusion
Disclaimer: XT shifter is being used with Ultegra RD, while X9 shifter is being paired with X9 RD. These different derailleurs may contribute to the difference in feel when using the shifters.
Both the XT and X9 shifts extremely well, both up and down the cassette. On the repair stand the X9 shifts better, but when riding the bike, both of them perform flawlessly.
The XT shifter is smoother, so smooth that sometimes I hardly feel the shift. The X9 has a more definite click when shifting, thus I always know when it has shifted. This tactile feedback is helpful as the X9 shifter does not come with gear indicator, while the XT does. I'm slowly learning to shift by feel and not refer to the gear indicator.
Also, the XT shifter mainly uses the thumb-finger combo to shift gears. Its quite good, as the thumb gets to rest sometimes. The instant release of the XT upshifting is really good, as it shifts almost immediately without waiting for the lever to recover.
On the other hand the X9 shifter uses thumb-thumb shifting, which is good in another way. For me I can switch easily between these two types of shifting, while some people cannot switch easily.
Both the XT and the X9 are almost the best that Shimano and SRAM has to offer for MTB shift levers, with the top end being XTR and X0. It is commonly said that the difference between XT and XTR (and X9 and X0) is the finish and presentation and price, with the shifting performance almost similar. Thus the XT or X9 is a good choice for those looking for top performance without the top end price.
If you want to use a Shimano road or MTB derailleur, get the XT shifter. Else if you like SRAM, get the X9 shifter and derailleur. I can't really recommend one over the other, because they are both excellent. If you die die need a gear indicator, get the XT. Also, you can choose based on your shifting preference (thumb-thumb or thumb-finger) or any good deal that you may come across.