Damn ! Did you actually spell his name right ? Well I gotta go with the Superman of the 5th Dimension here. Just think of it like this Mr. Mxyzptlk is an imp from the 5th Dimension which could crush Galactus if he wanted too... so I couldnt imagine what a Superman with 5th Dimensional powers can do to Galactus
I know I wont be able to convince you people of anything, but you give the 5th dimensional imps way too much credit.
Here is a nice bit of comparison for you (although it still does not constitute proof).
In the DC/Marvel Crossover: Superman vs. Silver Surfer - Myx's power alone was insufficient to breach the Marvel Actuality - it actually took both him and Impossible Man working together to do it. Impossible Man is indeed a nifty character but ultimately weak in the scheme of the Marvel Universe and by his vary nature he would be at least a 4th dimensional being (maybe 5th?) in the DC universe. But in Marvel he is really pathetic in the power scheme.
Everybody likes to quote and post from the comic that had Bat Mite and Myx destroying the universe and kicking the crap out of Spectre - here is the thing - IT WAS A JOKE COMIC (a.k.a. APRIL FOOLS TYPE!). It was not cannon - or if some moron over at DC actually made that cannon than DC in my oppinion has absolutly no balance, continuity, consistance or structure and should never be compared in any battle thread.
I mean think about it if it were true and Myx>Spectre what are 6th,7th,8th,9th,10th dimensional beings like. Hell with this mode Myx=5th, The Presence=6th, DC writters =7th, DC Board of Directors=8th, US Govt=9th, and our universe itself (the real one)= 10th. There is some back-assward logic for you - but it fits.
Also, DC's concept of Omnipotent is way overused, every pathetic worm in the DC universe is labled as Omnipotent - which in you minds seems to mean they can do anything. Well yes that is the definition of Omnipotent but you can not have a universal structure with so many things that are truelly Omnipotent or the entire Actuality of DC would be a chaotic nightmare of nothingness. IMO - to make the DC concept of Omnipotent actually work you have to understand that there are levels to it and I beleive that many things in the DC Actuality that are labled Omnipotent are not! They just seem that way because DC writes their comics from the view of a 5 year old (idealistic, perfect, good guys always win).