For this plant, excellent soil drainage is more important than hardiness in Portland. Ours lasted two years before not regrowing the next spring, but a neighbor's on the corner nearby on a small slope has done well for at least 5 years, and others in the area last several years or more. I have noticed on some plants a tendency to revert from the bi-color (red+white) to one or the other color predominating.

Does the depth of root during planting matter ?

It actually forms a largish (4' tall - 5-6' wide) semi-evergreen shrub. As with all salvias, good drainage and lot of sun is a requirement but IME, it is fully winter hardy here.......I've grown it for going on 10 years.

As to the flower coloring, it starts out with an almost uniformly solid red flower that progresses into the bicolor white/red for the bulk of the growing season, then fading to mostly pure white flowers late season (fall). Mine have gone through this color progression routinely every year.

"Fully winter hardy" if 10 years is considered an adequate trial period for a woody plant - in an area where the last serious thinning of the herd occurred back in 1990.

Since the average lifespan of a landscape (except for trees) is generally considered 5-10 years (landscapes switched out or renovated with a change in home ownership), yeah, 10 years is a very reasonable assessment of hardiness. And climate events like the winter of 1990 are not commonplace anyway.

btw, that would be herd, not heard.

From cistus.com, the web site of Sauvie Island based Cistus nursery, the home of zonal denial (if they say something has hardiness issues, well...):

Best grown where heat accumulates and not much summer water is provided. Frost hardy into the mid-teens F, mid USDA zone 8. Protect from winter extremes.

I'm not sure there is much in that remark that contradicts what I stated. Survived unscathed the low teens during the winter of 2010...........

OP has unanswered question. The final potting should be in a multi-gallon size container and even then you will have watering and protection from hard freeze duties more often than if it is put in the ground. If it is looking good in the original pot, plant it at the same depth. Try to avoid flat ground or else mound up some soil. Any standing water near this plant is potentially bad.

After reviewing replies so far i am inclined to plant in the ground at a location with a gentle slope, next to a small underground drainage duct and full sun.

Mine is in its third year in the Portland 'burbs. Fred Meyers sells them every year so they are inexpensive to replace. I started out with a 4" pot and it's a 3' shrub now, plus it was moved after its first summer.

That is good data.

January 2017, I recollect Portland was down to low teens probably even lower.

Key is the drainage, it appears.