Given ages of Tobi Roppo, most of their bounties don't reach 300 mill imo. Oven/Daifuku were at 300 million and they were 48.
For the weaker trio, I'd say
Page One - 200 million
Black Maria - 200 million
Ulti - 250 million
For the stronger trio, I'd say
X-Drake - 360 million
Sasaki - 390 million
Who's Who - 400 million
Lol, what? Ulti is not "far stronger" than pre-TS Luffy. Luffy took down a Shichibukai (actually 2). Ulti stands 0 chance against Crocodile. He took down Enel, who Oda said would have had a 500 million bounty, which would have been the highest bounty shown in the series back then. Even Rob Lucci was as strong as the strongest Vice Admirals like Doberman, who said there's "nothing he can do" if Lucci is fighting Luffy.
Like I wrote in the other thread, Moriah could fight the Mid Tiers of Whitebeard's crew like Curiel. Luffy could fight/beat these guys. He even told Ace "one of these days I'm going to surpass you". Only guys Luffy couldn't beat in Whitebeard's crew were Marco, Jozu, Vista, Ace (although with enough plot armour I wouldn't rule him beating Vista out).
I don't totally disagree with this, but I don't agree with it either.
I'd personally say that Page One and Ulti, who are big guns in Kaido's crew and are likely really infamous as pirates would have 300 mil minimum. I think 300 mil is the good starting point for most fighters who are considered "monsters" in the new world. Just because they're young doesn't mean they aren't accomplished.
I pretty much agree with you on the bounties of the other flying sixes.
I could see a few of them breaching 400 million, but I don't think they'd have bounties higher than Jinbei's currently (438 million).
Of course, this is just speculation, but I think its appropriate considering what we know about them.
400 mil bounties are incredibly impressive.
As for pre-time skip Luffy taking on characters like Ulti. I think he'd be able to put up a decent fight, but he wouldn't be able to win or beat someone like Ulti by himself.
Here's how I see. Lets use Oven instead of Ulti to demonstrate this point. I could see the strawhats managing to take out Oven as they were pre-time skip, but I don't see any of them doing it alone. I think to take out veteran level heavy hitter pre-time skip, the strawhats would seriously need to pull all their stops out and work together to stand any chance. Even then, they would be just as or more drained from that than after fighting someone like Oars or the Pacifista(definitely the pacifista at least).
By himself, I think Luffy could accomplish a bit, but not too much. Like, if you were to place pre-time skip Luffy up against someone like Oven, I think he'd be able to land some good hits, bring Oven to his knees like he did for Magellan, but I don't see pre-time skip Luffy winning that fight.
Against Ulti, unless they had some great plan, I don't think their power alone would be enough to bring Ulti down. Ulti is an ancient zoan, which are known for being stupidly tough.
Luffy pre-time skip would probably land attacks strong enough to hurt Ulti in gear 2nd but I don't think Luffy would be able to put someone like Ulti, who is emphasized for their toughness, down pre time skip.
I think pre-time skip Luffy in gear 2 would a decent enough challenge for veteran level fighters, but I don't think he'd stand a high chance of winning(though I think he could if given the right circumstances).
Gear 2nd's most valuable attribute pre-time skip. At least during marineford, was its agility, and I think his agility would be what makes him a challenging opponent for veterans, if he ever fought any veterans from the new world pre-timeskip.