What other calibers would you run through the suppressor? Some 9mm suppressors will run supersonic 300blk. Many use 45 caliber suppressors for caliber flexibility.
When I worked at a gunshop, traces were only phoned in by the BATFE. I remember sighing everytime I'd see that West Virginia number come up on the gunshop's caller ID.
The only people that can really get that info is BATFE and I think it's only for official business.
If you shoot the 43 with accuracy you are happy with then I would not get the 42. The 42 is just a little bit smaller and I think its not enough to be an CC game changer.
My experience is most rifles that have optics aren't mounted with the optic that person really wants. The more customized it is, the less people want it. Sell it separately.