Optimal Target Speed for Fortress Shields

A Fortress Shield grants +3 to AC instead of the normal +2 for raising a regular shield, but costs 10ft of movement. So basically, +1 AC for 10ft of movement.

Given the relative equability of this trade deal, it's probably safe to assume we're already wearing full plate. but meet the strength requirement for it, so we're suffering a total 15ft movement speed penalty. This would bring most folks down from 25ft to a 10ft snails pace.

Pathfinder2e being relatively balanced as it is, any variety of feat such as Nimble Elf or Fleet boosts our movement speed by 5ft per feat, with one exception.

Unburdening Iron lets us ignore our armor's penalty, and reduce one other penalty by 5, netting us 10ft of movement. Though, as a Dwarf, we have a base 20ft move speed which is quite slow.

Adopted Ancestry would let us pick that up, but at the cost of a general feat and a racial feat it's not much different than just taking fleet

Cultural Adaptability would let us poach unburdening iron in naught but a single feat. Samsaran get a similar feat Remnants of the Past but it doesn't let us pick a racial feat, so it's no better than picking up adopted ancestry normally.

Elves have a native 30ft movement speed and access to the Nimble Elf feat, netting us 20ft after penalties compared to the dwarves 15 feet with Unburdening Iron.

Our maximum potentially would be to take a custom mixed heritage to be a half dwarf elf, then picking up both Unburdening Iron and Nimble Elf netting us a 30ft move speed after the remaining 5ft penalty, being quicker than anyone who didn't pick fleet, though we could do that too bringing us up to a net 35ft speed.

Which ultimately begs the question of when to quit.