The 24 inch and 30 inch XXL CSO have the same interior dimentions and capacity. Unless you have another reason to make your cabinet 30 inches I don’t see any advantage to the wider oven. If down the road you would want to stack it with a 30 inch wall oven during a major rennovation that would a reason to go with the 30”. They use to sell a trim kit for the 24” ovens to fit a 30 inch cabinet - do not know if they still do or not.. Are you keeping your 30 inch oven? From you post it sounds like it. As an FYI = I think you find that reheating food in the CSO is far superior to a microwave.

The eleven expensive Miele XXL steam ovens range from the 24" DGC 7860 ($6800) to the 30" DGC 7780 ($7800) to the DGC 7885 ($8300). It's not clear that there's any difference in the cooking capabilities of these appliances. I'd read the user guides before selecting.

Prices differences are due to 24” versus 30”, plumbed versus non-plumbed, and user interface. I recommend the M-Touch interface as I find their automatic programs to be very useful for their steam oven. I also suggest purchasing an extended warranty as this is a fairly complicated oven and I had several repairs on my first oven until Miele deemed it unrepairable after 9 years of use. Miele replaced it with a newer model version (same exteriror design) for a very good price.

• Fisher & Paykel OS24SDTX1 24 Inch Combination Steam Smart Electric Wall Oven ($3300)
• Dacor DOB30T977SS 30 Inch Single Steam Smart Electric Wall Oven ($4000)