extractors fitted to a 2004 GXL prado 4lt

I'd suggest no... why? because extractors potentially can save fuel, but they also let you use it when you plant your foot and release the increased neddies!

check www.pradopoint.com

There is no one answer to this question. My first question would be what sort of gains have been made by fitting extractors and exhaust, you wouldn't just do the headers. Do get back the savings on fuel and the total spend you would need to do another 100,000kms at a guess. For example if you were to buy the diesel cruiser over the petrol mode, for around $10k more you won't save on fuel until 250,000kms and above. If you don't care about fuel and want better drivability then this is a separate issue. You may detract from your re-sale value of the vehicle by fitting a complete aftermarket exhaust, do you care about this.? The list goes on.

Typically no one mod alone will give tangible gains...a combination of extractors, exhaust, decent air filter and air intake may however. Depends on what you're after really. Power or economy.