I'd lean more to the GPP sizing than elsewhere, primarily because they tend to understate mature sizes to some degree and they are also local. Monrovia has generic info intended to be disbursed to the entire US.

It is only a slower growing, red barked form of the species so no reason to assume it will remain significantly smaller than the species over the course of time. And these can get quite large, given enough time and good growing conditions. The Elizabeth Miller Garden in north Seattle has vine maples that are easily 25' tall and as wide, but they've been in place for 50 years or more.

A local gardening friend has had a Pacific Fire for about 10 years and it's approximately 12'x12'. This cultivar tends to be most often presented in a single trunk form rather than the multi-trunked, shrubby species vine maples found at most nurseries. That aspect would also tend to promote somewhat taller growth

The largest, shade grown vine maples drawn up by forest conditions are over 60' tall. Growers seem to have gotten pretty fast growth out of 'Pacific Fire', judging from stock I have seen offered. Ones maybe head high or taller have already been presented at local outlets. So I definitely don't consider it a dwarf.

Clump or forking examples of various trees growing in groves are typically as tall as their single-trunked brethren.

Thank you Embothrium and Gardengal. I will assume the larger sized mature tree and plant accordingly. Maybe I'll check back in 10 or 20 years and let you know how it went!