Hmm I'd argue that we are of similar size to Bolton, if not we are bigger. They haven't done anything since the 50s.

I'm tough. I'm ambitious. I know exactly what I want. If that makes me a bitch, I'm OK with that.

They're a similar to Preston, who are also bigger than us.

All mentioned are either big city clubs or have absolutely no competition for fans within a 50 mile radius. This does not make them necessarily a bigger club. Wednesday are bigger because they have a bigger stadium, bigger gates than us (even in the Championship) and have spent longer in the top division in recent years. Forest are because of their gates and the trophies they have won. They were actually a similar sized if not smaller club than us before Clough arrived there.
Leeds and Birmingham City are big city clubs with little/no competition for fans and have trophies so I would say they too are (at the present time) regarded as bigger than Palace. Ipswich, Bolton and Blackburn though are most definitely smaller than Palace. Blackburn is a small town with low gates, Ipswich is a big town but still have (comparably) low gates for the area/Norwich being their closest rivals. Bolton have always been a small club. Their prolonged period in the Premiership enabled them to build (with funding help from Reebok) their new stadium and with Premiership football often managed to fill it but not always.

I think "big-dom" has a shelf-life, personally, which lasts something on the order of two decades. If you've been "big" in recent memory then you are big...if you haven't, then at some point you just stop being big. The bigger you were in your big period, then the longer it takes your bigness to dissipate once you fall on hard times. There are small handful of exceptions (Man Utd will pretty much always be big no matter what) but outside of that...not many.

In light of the above rule:

Sheffield Wednesday = not big. They haven't been relevant for decades. Their bigness was extended by Hillsborough being an FA Cup Semi Final ground but even that's no longer so. Now, average team with big (and empty) stadium.

Nottingham Forest = now clinging on to the last vestiges of the bigness they achieved under Clough. They have about another 5 years left to go back up and re-establish themselves or they will become another Wednesday...a big club at a low level but not a big club.

Leeds = have a touch of the Man Utds about them; fundamentally big so it will take (or is taking) a little longer for their bigness to wear off. By far the biggest of the teams in your list.

Derby = See Sheffield Wednesday. Weren't really ever big in the first place.

Leicester = See Derby.

Ipswich = See Leicester.

Bolton = Haven't been big since the 50s. Even in their Premiership years, they weren't big. It's over half a century since they've been anything but an average team.

Birmingham = See most of the above.

Blackburn = I think a lot of their bigness comes from the Jack Walker years rather than from history. Still, they became big and are just about still are because that was only a decade or so ago. Give Venky's a couple more years and they'll be back where they came from in the 80s.

So, to me of the teams you mention, only Leeds are really "big". The rest are what I would call, like Palace, "big small teams", not "big big teams". The funniest thing is deluded Bolton-type supporters who are given to pretending their team is further upmarket than it is.

Sydenham by birth. Selhurst by the Grace of God.

You never forget Yeovil.

They don't have to be big-big, Syd. We are comparing them to a south London club that's nearest feat to domestic silverware is an FA Cup final appearance, and a club that has always had average attendances throughout most generations.