We need to clear up what section of exhaust you are getting done. Axle back suggest just the rear section which will make relatively no difference to power and may give you a louder car. Also will have no impact on back pressure. Cat back would suggest a centre section and rear section leaving the standard downpipe and cat in place. That will give you much more noise, small power gain but again little to no difference on back pressure. Turbo back is basically the full exhaust system and having no cat in the downpipe will give a large power gain, take away a lot of back pressure and depending on boxes in the centre and rear will make it much noisier. If you are having a full system with no cat in the downpipe it will need to be mapped. For centre and rear box changes mapping is not essential.