I know that CU Amiga was selling close to 60,000 copies a month at one point. Try contacting the publisher of the magazine to see if they can provide you with sales figures for some research your doing. I'd say that it's a fair bet that if magazine sales are anywhere near the 20-22,500 mark, more than 45,000 machines were sold.
To put that in perspective, Amiga Format sold over 160,000 copies per month at it's peak in the UK. This was under two years before the demise of Commodore and at a time when the UK also had a few others selling in the high tens of thousands and even more selling in the lower tens of thousands a month.
Looking at that and the supposed UK sales figures, I'd say Benelux sales were way higher than 45,000.
