Hayward and Scott design bespoke systems and they have always performed exceptionally well for me - a full tailored system fitted to my SL would definately be well under £1000 ( I asked 3 or 4 years ago when i discovered an MB system would be £1200), and I would be pretty sure it would deliver the goods as well as far as performance is concerned.
That said there are many such as Talbir who prefer the OEM AMG authenticity - surely its each to his own and has already been stated the market will dictate its value as and when it comes up for sale again
Mark