Ken,
For me the question divides in two parts:
i played with an extension only 2-3 times when I was bass-shopping outside of germany. We have hardly any basses with extensions here, only five-stringers. I´ve never seen an extension in a german proffesional orchestra.
A pic of my 5er is attached.
With this bass I played the LvB 6th severals times.
Regarding my limited comparisons I think it will be much more easy for you to use your hungarian 5-string bass, because the ways between the notes are much shorter, it´s much easier for the left hand to move 1-2 inch between the 5 strings than to move all along the extension.
Regarding the string spacing: it´s just a matter of practice I think, and maybe you´ll need less practice-time for this, than you would need for trying to play the semiquavers with the extension.
I think the “storm” is a kind of special effect with the methods of the 19th century. To make it sound like a storm it´s not necessary for the bass-section to play all notes in time and tune.
The effect is achieved if the basses
try to to this…
I´m not saying to fake it, I think it´s important to practice the part as best as you can (if the conductor let´s you play it alone, you know why…)
But if you listen to concerts of very good orchestras it always sounds a little bit more like “storm” than like a highly precise machinerie, and I think that’s what beethoven wanted.