First of all, what is the brand of the current piggy back u r using? Usually, piggybacks are able to by-pass the speedcut limit.. why is this not so? what was your intent of putting in the current piggy back? has it achieved your original goals? I am assuming the below are the main 4 factors:
1. Performance
2. Safety
3. Reliability
4. Value for Money
Basically, nowadays the stand alone engine management system is 'almost the same'... except for Syvecs.. however, that's like.. freaking expensive. No matter what you choose, fundamentally, it depends highly on your installer and tuner. Installer will ensure the 'safety' portion of it - no burning, no shorting, no signal losses - intermittent or otherwise which in terms, influences reliability.
Performance depends highly on your tuner - streetability, fuel economy, WOT sessions and of course, your speed cut(??)... all of these will sum up to - value for money.
Even full stand alone engine management system, for most - they will piggy back on to your original ECU but taking up most of the engine monitoring functions (by passing the original signals).. however, the gearbox and aircond will still remain.. I'm not sure about Mark X though.
What sort of figures / budget are u looking at?
Word of caution - there are hundreds of tuners out there who can promise you the world. Get those that has been proven - not those that can talk. Not many can walk the talk.. just talking the talk.
Thanks
