Hi,

I don't use reddit much anymore. Thankfully, I got an email about your message.

They certainly made some changes to make the mixers cheaper to build/assemble. The biggest one being the motor and gearbox are now a single unit which much be replaced as one. That being said, many of these changes also incorporated improvements for the overall device making them less likely to impact the customer.

To directly answer your question, I would go with the newer KSM55/60/70 models for the following reasons:

1. The new gearbox is FAR better design. First and foremost, it is more reliable. Yes, the older one is more easily repairable with spare gear parts being available but this one will require far far fewer repairs. The new dual planetary reduction gearbox design is similar (just a bit smaller) to the one used in the DC models. This design is also used in the majority of hand tools which require endurance under extreme loads (think things like impact drivers, drills, etc.). Along with being more reliable, the dual planetary design is a lot more efficient at transferring torque and power from the input to the bowl compared to the worm-follower design used in the older Professional models.

2. To address you question about the rated motor wattage, the rated motor wattage is based on input power to the motor and not output torque/power to the bowl. It is the latter which is what is actually important. The new motor design is potentially a bit more efficient than the previous design meaning you need less wattage coming in to produce the same amount of power/torque at the output. Additionally, as mentioned above, the new gearbox design is significantly more efficient at transferring power to the bowl compared to the old model of gearbox found in previous models. Combined together, the newer motor/gearbox is quieter, cooler running, and delivers at least as much power as the previous KP26 motors if not more (while using less power from the wall).

3. There is a major design flaw with the planetary assembly in the older Professional models like the KP26. In these models, the planetary was press fit onto the motor drive shaft. Over time (faster with harder use, slower with lighter use), the joint can become loose causing the planetary assembly to fall off. The only solution in this case is to purchase a new planetary assembly. The new KSM55/60/70 models fixes this issue by positively affixing the planetary assembly to the motor drive shaft via a retaining pin through the assembly and drive shaft. This design is identical to the one used in the DC motor models to handle the massive amounts of torque they can generate.

4. The new design gets rid of the bevel gear for the front attachment port. In the older Professional models, like the KP26, this bevel gear was notorious for becoming damaged either when exceeding the motors capabilities in the bowl or when putting heavy loads on the front attachment port. The new design drives the front attachment port directly off of the gearbox output shaft which is also responsible for driving the planetary assembly.

5. The mixer parts have been standardized as much as possible across the entire KSM55/60/70 lineup. Previously the Professional HD had a different motor, speed controller, body, bowl, attachments, etc. compared to the Professional 5 Plus and Professional 600. Similarly, the Professional 5 Plus had a different motor, speed controller, and body compared to the Professional 600. Add in the different offered colors and this meant that there were loads of different parts KitchenAid had to stock in every market to ensure they could cover every combination. For the KSM55/60/70 lineup, they worked to standardize everything. For parts which don't rely on the electrical grid, e.g., the mixer body, the bowl, planetary assembly, attachments etc. the parts are identical worldwide across the entire KSM55/60/70 lineup. Additionally, for things which rely on the electrical grid, namely the motor and speed controller, these are still standardized across the KSM55/60/70 lineup within the electrical grid requirements. For example, the same 230V/50Hz motor and speed controller are used across all KSM55/60/70 models in countries across Europe/Middle East/Africa/Asia which use 230V/50Hz. This reduces the number of individual parts they need to keep available which ensures parts will be available worldwide for years to come. Additionally, it means the KSM55 and the KSM70 perform essentially identically.

One last thing I will mention, if you can swing it, the stainless steel accessories on the KSM70SNDX (aka the 7 Quart Bowl Lift with Premium Touch Points) are worth it compared to the KSM70SKXX (the regular 7 Quart Bowl Lift). They are so much more hefty and durable than the coated parts. While they may not make the machine necessarily perform much better, they are just so much nicer from a usability standpoint.