(63 yo / 5’10” long in the torso / 140 lbs) – In January I ordered both the Zpack Pivot Solo, and Altaplex. I tried them both sitting on a 3″ Thermarest pad. I found the Pivot Solo felt slightly roomier. I didn’t brush my head on the ceiling of the Pivot Solo sitting up, whereas I did in the Altaplex.
I feel the usable length of the two seems about the same, but I did NOT employ the end pullouts on the Altaplex, so I have to believe it would be slightly longer – theoretically – though I sort of fail to see they would make a huge difference – could be wrong there. The tall mesh end panel of the Pivot allows you to really scrunch up to that end without touching the ceiling, and I prefer my head on that end. Mids lose a lot of their theoretical space due to their steeply sloping ceilings, creating a tight pinch point at the feet, head, and shoulders when sitting up.
If the Altaplex was the only one available, I would happily choose that, however for a 1 ounce weight penalty of the small 32″ carbon pole required to create the Pivot, I went with the Pivot Solo – I just don’t like the interior feel of mids, and prefer the L-shaped door, zipped vestibule, and lower pitch of the Pivot Solo. It also requires fewer pegs to pitch. I know it’s not quite “technically” a 1 pole tent, but it’s close enough as it takes only one trekking pole which was my criteria also – I don’t do two trekking poles, but rather use a single staff.
I can’t claim to know which would work for a guy your size, but I’d suggest you order both and try them both. I paid the extra to be able to return either post/hassle free. I did take care to set them up on a piece of Tyvek to preserve them both in new condition when putting them up outside. It became very clear to me I preferred the Pivot Solo.
However, for general backpacking, and if I still bike toured, I’d think long and hard about the TT Rainbow Li or Rainbow 2P Li. More interior spaciousness than either the Altaplex or Pivot Solo, simple to pitch, and meets your criteria of a one pole design, while still being very light.