Among other things I run a K1200 I'll cut the story as short as possible but I actually have had 3 different pipes on it a Remus/Laser and an Akrapovic and what I learned even after all these years not all pipes run the same they were actually miles apart in how they altered the character of the engine.

Have a look at the steady stream of bikes that appear on here that have all been the same route that's a named exhaust/filters/snorkel out and PC fitted now if your looking for the best results from your 660 that's the way you'll get it,now if folk can't afford such and at one time or another we have all been there then one has to settle for less it's just ironic that in the long term ownership of a bike the cheap ways always turns out to be the most expensive because you will end up replacing the original cheap options.

Keep stock till you can afford it,as for buying new? I do from time to time but most of the pipes I buy have been secondhand let someone else take the loss.