If you go on the EPC which lists the genuine springs for all models, you will be surprised at the number of variants in the listings. Having tried various makes, there is no substitute for genuine original spec springs. Many manufacturers have a 'one spring fits all' approach, which invariably results on an incorrect ride height - usually jacked up at the rear like a dragster.
If your car has self levelling suspension then the original springs are softer but are compensated with correctly working rear shocks to maintain the correct ride height even under load. If you put a stiffer spring from standard sispension this can give an incorrrct ride height.
Personally, although more money, I only use genuine VX springs to ensure the car sits as intended.
Some on here will poo poo this, but if other than the genuine springs are fitted, you cannot guarantee the back end will be correct.
If it does have self levelling, the compressor needs to be the checked to ensure it is working correctly to maintain the ride height, although being a CD spec it probably won't have.
I have tried various options of springs in the past, but always gone back to genuine.
Just my thoughts based on my own experiences.