Chocloate box kid
Sorry, I have to disagree with you although I am at fault for not really explaining that I believe Portsmouth have also been one of football's under-achievers.
Of the teams you mention, only Forest have won a sizeable amount of silverware and this is almost soley under the auspices of Brian Clough. I my opinion this is probaly the greatest set of achievements by a Provincial club. Ditto Derby under Clough.
Other than a league Cup win under Martin O'Neill, Leicester have achieved little. Ipswich flickered briefly under Sir Bobby Robson but quickly reverted back to a provincial club. As for the others, they have very little pedigree. Middlesborough have woeful attendances and are very much a second string team on the North East. It's easy to forget but Portsmouth are a club that has engendered support worldwide through the Royal Navy (maybe more in the past as our maritime presence has shrunk to reflect the country's diminished stature in the world) and , had it not been for Hitler, are alleged to have been so strong as to have dominated English football in the early forties as well as the end of the decade when they oicked up two , successive titles. I think you will find that they also provided the national squad with several players at this time - a feat later repeated in the 2000's when they had James, Defoe, Johnson, etc, etc. Culturally, Portsmouth are an important club. Part of Clough's aura was the fact that he achieved success with provincial teams that had hitherto made little impression on a national scale. I am no expert of Portsmouth's honours but this link should give you an inkling of their record:-
http://www.portsmouthfc.co.uk/club/honours.aspx
It would be curious to compare this with a club such as Newcastle United - I wouldn't think that there is too great an amount of difference in the amount of trophies won between 1945-2011 or atleast not out of proportion to their respective "perception" amongst football fans.
If you want to make a comparison with any football club, Portsmouth should be measured against a side like West Ham - i.e. A great tradition and solid working class support yet only sporadically obtaining their potential. I have supported Southampton since 1974/5 and have no affinity for our South Coast neighbours but I still wouldn't deny them a "big club" tag. It would be fascinating to see some of the analysis that the writers Kuper and Syzmanski applied to England's international win record to assess Portsmouth. I feel that this would demonstrate that Portsmouth have effectively under-achieved. In my opinion, they are a sizeable club (certainly from a "cultural" point of view if nothing else) but probably have substantially underperformed in the last 50-odd years. I would also add that the respective owners have also had a very regressive attitude concerning the way that the team has almost consistantly been mis-managed by the numerous proprietors. This has certainly left them languishing in the past in an antiquated stadium and non-existent training facilties. As much as it pains me to say it, Harry Redknapp definately knew how to unleash the potential of this team - a reason why their continued fall will be more spectacular than our own.