FWIW, the top tube on my mountain bikes, even when taking into consideration the differences in HTA are longer in the TT than my road/touring bikes.

I have the Myka in the non-disc version. It would be fine for your purposes unless you ride in wet conditions a lot. My only complaint with the componentry (I'd have to check to see if this year's model is the same is mine) is that it was VERY hard to shift between chainrings. Going from bigger to smaller was fine, but smaller to bigger was very hard.