Un responsable de chez Digitech avait expliqué la différence de puissance entre les 2 appareils, le RP500 est 2 fois moins puissant ce qui a une répercution sur les sons. Surtout ceux qui demandent beaucoup de ressources (comme les réverbes et les modelisation d'amplis par exemple)
As for the difference in chips, let me use this example. During my tenure at Lexicon I sold quite a few 960L reverbs to high end facilites. For those not familiar, the 960L is Lexicon's flagship reverb processor that comes in around $15K US. Lexicon also sells a variety of mid and lower priced reverb units. Here's my point. The Large Hall or Small Church algorithm that's in the less expensive units is the same one that's in the $15K processor, the differernce is the processing power behind it. To do really high quality effects (especially reverb) you need alot of processing power. It adds a definition and transparency to the effects not found in the lower priced units. That's the difference between the RP500 and the GSP as far as tones. Pretty much the same amp models and effects, but the GSP has twice the power thus more definition to those models. Add that to the fact that you can power those models with your amps power amp section and you now have a deadly combination. This does not take away from the quality of the RP500's tone, just remember it's half the processing power for half the price.
D'autres gros points forts du GSP par rapport au RP500 : les possibilités de connectique, le seamless branching (je pourrais plus m'en passer)...
Mais je suis certain que le RP500 va quand même être un pédalier excellent.