So, first off, Perron probably doesn't belong in the discussion, seeing as I was talking about top 6 forwards and whether Giroux belongs. I don't think Perron is in our top 6, so why even bring him other than to be a strawman. Moving the goalposts to shit on him is just that, goalpost moving.
Perron though, as I said, is tough to gauge, he certainly hasn't lived up to his contract, but there is some significant context that goes along with that, which may be short term context. This season to me is a write off for him, I don't think he'll get full value for his deal next year, but I do think the odds are that he is closer to providing full value than he was this year. Time will tell but either way the deal didn't work out, at least on ice.
Giroux on the other hand, I think his deal has been great. He's an effective penalty killer, a faceoff demon, produces well within top 6 numbers even still, and isn't a complete liability defensively. We're in the last year of it, so it's at it's worst in terms of value to cap hit, but even then, it's only slightly overpaid compared to the market in terms of his in ice impact. That said, the rumour right now is he's going to extend for around 4.5 which would bring him well under market value (assuming his play maintains, it may regress).
All that said, both players bring more than their on ice impact, they are both experience vets and are in large part here for that. I don't think you can easily quantify the impact vets have on a team, and we specifically went out and targeted that for a reason. Giroux clearly can still play, and has a wealth of experience, he is exactly the type of vet we should want to have around the team. Perron, it's a bit more dependent on whether he can get his play back up to snuff. Bad backs will wreck your game, so who knows.
It's also telling that you ignored guys like Rodrigues and Compher, and we're currently limiting comps to only SC winning teams. The reality is lots of teams would love to have Giroux in their top 6, people are absolutely delusional to think otherwise.