io per ora non ho tempo di provare, ma potrebbe essere interessante:
% \subsection{Big Integrals}
% \LaTeX\ does not treat integral signs as variable sized symbols,
% in the way that it treats delimiters such as brackets. In common
% with summation signs and a few other operators, they come in
% just two fixed sizes, a small version for inline mathematics, and a
% large version used in displays. In fact by default \LaTeX\ always
% uses the same two sizes (from the 10\,pt math extension font) even if
% the document class has been specified with a size option such as
% \texttt{12pt}, or if a size command such as |\large| has been used.
%
% The standard \textsf{exscale} package loads the math extension font
% at larger sizes if the current font size is larger than 10\,pt.
%
% The HTML3 math description explicitly states that integral signs
% should be treated like delimiters and stretch if applied to a large
% math expression. By default this package ignores this advice and
% treats integral signs in the standard way, however an option
% \texttt{bigint} does cause integral signs to `stretch’ (or at least
% be taken from a suitably large font). The standard Computer Modern
% fonts use a very `sloped’ integral which means that they are
% not really suitable for being stretched. Some other math fonts, for
% instance Lucida, have more vertical integral signs, and one could
% imagine in those cases making an integral sign with a `repeatable’
% vertical middle section so that it could grow to an arbitrary size, in
% the way that brackets grow.
ciao
f