In UK English "milliardo" is a milliard, in American English it is a billion; it can also legitimately be translated by "million" or "thousands" or even "an awful lot (of)".
since they state "millioni di milliardi" it really is an awful lot!! But since it is a business/financial article, I would suggest using "many millions" - although technically it is a "million milliards" (UK) or a "million billion" (USA)

I think trillions id a large enough number to be understood (sort of) and still be overwhelming. Millions of billions are actually "quintillions" (10 to the 18th power).

...if you weren't happy with just "billions", which is fine IMO.

trad. di "milioni DI miliardi" (con 6041 riscontri in rete! )

I believe several and many sound too small. Contless/unlimited too vague loosing the impact of the original expression. Trillions, etc, mathematically correct but also a different style.
I agree that millions of billions sounds weird, so let's just pitch in three extra figures :-)
Milioni di miliardi sounds OK in Italian

I'd just leave it at that

a billion (in UK) is a million millions (10 to the 12th power); a thousand billions, then, is 10 to the 15th power (just like "un miolione di miliardi) - and IMHO doesn't sound too ridicolous or offensive to the hear. Since a billion in USA is just a puny thousand millions, I'd add the figure in parenthesis to avoid any doubt.

I think that a vague statement such as "many billions" wouldn't do very well: when speaking of the number of (financial, I gather) operations a system can handle, a 100 or even a 10-fold difference can be rather important in assessing performance.

BTW, both quintilions (10 to 30th power - !!! - by my Concise Oxfor Dict.) and trilions (10 to the 18th power) seem a bit too much to me...