If Trouba was willing to sign 7 years, I'd go maximum 5.5
7 x 5.5 = 38.5 million.
I wouldn't go more than that. Because as much as some people love to hype the guy, i just don't think he's shown that he's worth it yet.
I think your valuation is reasonable. Trouba hasn't shown much (or had the opportunity to show much) that should put him above that amount. I don't really think Jones is fully in the discussion as a comparable, he'd be the upper absolute boundary. But with any of these negotiations you're buying up UFA years on speculation so they'll cost more driving the AAV up.
Also still think we're seeing a shift in where the max value contract for players will be going forward. It'll be one of two deals, when they are coming off their ELC, typically with 4 years of RFA left. The second will be when they're coming out of that RFA/UFA combined deal they signed.
Eight year deals will favor the teams in the sense that Trouba would be 28. Still young but you'll hear rumblings about him "being close to 30" during the next negotiation so you'll likely see shorter terms (5 years), maybe with higher AAV kind of like Buff's deal. A six year deal would favor the player - in Trouba's case (or Scheifele's for that matter) he's more likely to get a better, longer contract coming off a six year deal at 26 because the meme will be "just a year over 25" but at 26 the agent will be spinning it something along the lines of "well, at 30 you gave Buff a big deal for five years carrying him out to 35 years old, so my client being 26 will want an 8 year deal with similar AAV (would be nine but eight is max term). Six years and eight years gives a guy like Trouba 14 years of pay. Eight year deal out of ELC likely only results in a five year deal subsequently meaning he loses a year of term (he could sign again as a 34 year old of course) and probably overall a decrease in AAV.
So why would these guys sign an eight year deal? I can't imagine any agent thinks they are good ideas. Seven as you propose? Kind of that compromise where maybe you get consecutive seven year deals. I think if I'm a player with no loyalties early in my career then I really only want to sign a six year deal. And that's not to cast aspersions on Trouba's loyalty or not, it's just good business sense.