My first opinion is that your specimen was M. scutellatus.
This is the more probably thing since you collected it in US.
But, if you see some differences, you must check if your specimen might be another (also introduced) species.

The main difference between M. scutellatus and M. sutur is that the body of the former shows metallic reflections, while the latter is completely opaque.
Your first pictures had clear reflections, the second two, not.
Secondly, M. scutellatus is marked with white pubescence, M. sutur with yellow one.
This beetle seems to me yellow.

Nevertheless, a picture may mislead.
You has this specimen and you can personally check it.

It should be rather a female of Monochamus carolinensis (Olivier, 1792) or M. scutellatus scutellatus (Say, 1824), well distinguishable through its different elytral pattern.
You can confront the types at: http://plant.cdfa.ca.gov/byciddb/thumb.asp?g=Monochamus

The elytral apex is teratologic, maybe due to an insufficient environmental humidity; therefore, the elytral spines (diagnostic character) are not well distinguishable.
Moreover, I can't understand if the insect is brown or the pictures have a yellow light dominance...

I would rule out scut*ellatus because the scutellum and elytral markings are a dull gold rather than the usual brilliant white.

I noticed the deformity but doubt there was insufficient humidity since the beetle came charging out of its hole in solid wood of a small dead tree that had normal moisture below the bark I was stripping.

I viewed the images on the CDFA site you linked to and have added it to the Monochamus Info page. While I agree that it is a female based on its "short" antennae and is therefore likely to be more parallel-sided (males are tapered from humeri to apices), I am still not able to decide on carolin*ensis.

I will shoot the (now) dried specimen in more detail this morning, including elytral apex and some shots in natural lighting.

(Un)fortunately the choice for a north-eastern Monochamus is not wide.
There are only: scutellatus, notatus, marmorator, caroliniensis and titillator.
M. notatus, marmorator, and titillator have a dark-light pattern, while your specimen has only the light pattern.
The other two species seem simple: scutellatus is black with white marking, caroliniensis brown with yellowish marking.
Moreover, scuellatus has mutic elytral apex and caroliniensis spined elytral apex.
If you still have got this specimen, you can check the difference.

in the detail images I'm uploading now. That puts me (us?) back to genus.

Could Say, Leconte and friends have missed a Monochamus species that might restrict itself to the Krummholz zone?

Dear Jim, by using Breuning's key to world-wide Monochamus I can reach only 3 species like that: M. scutellatus, M. impluviatus from Western Siberia and Korea and M. sutor sutor from Europe.
I have all these species in my collections and, after having confronted your specimen, I came to the conclusion that yours is a female of Monochamus sutur, or (less possibly) a new still-not-described species.

I only keep specimens in case they are needed for identification or desired by others. I would like to find out whether it is invasive or undescribed. (If the latter, it would be the second undescribed species I have found, the other being a euc*nemid.)

Anyway, email me a shipping address and it's yours for examination. Let me know if I should soften it and send it in alcohol or send it dried. I have an idea Don Chandler at UNH would like the specimen eventually if that is okay with you.

To me it looks like scutellatus. I would say definitely not carolinensis. True, the spots are yellow rather than white but the dark bronze elytra, boldly spotted scutellum, and no spines lead me to this.
I don't know how much can be made with the yellow rather than white and the shape is a bit elongate for a female. Another possibility to consider is a hybrid, possibly scutellatus x marmorator. Quote from The Forest Insect Survey of Maine, Order Coleoptera, Insect Disease Division Technical Report No. 32, Dec., 1993 by Dearborn and Donahue:
Most (Monochamus) are very distinctive and easily identified. However there is good evidence that natural interbreeding between species does occur and that hybrids are occasionally collected. Good series of forced hybrids and back crosses (F1 and F2) are available for study in the insect collection of the Entomology Department at the University of Maine in Orono.
I think the reference they list for this is Fickus, T. P. 1956. The sawyer beetles in Maine. Orono. Me. Agric. Exp. Sta. Maine Farm Research. 3:14-21, but I haven't seen that paper or the actual collection in Orono.
Still, we'll keep hope that you've discovered a new white mountain endemic as that would be very cool.

I think I'll see if I can get an opinion from Dearborn on these images.