I made a current comparison, sadly I forgot to measure/write down the boot times, and now my Pi is back in production. Better then nothing:
Test system
- Raspberry Pi 2 Model B
- CSL 5V 2.1A power adaptor
- Kingston SDCA3/64GB U3
- Raspbian Stretch based system
- direct terminal access via monitor and keyboard
After comparing both available systems, I used the PREP_SYSTEM_FOR_DIETPI.sh script to upgrade Raspbian Lite base image to DietPi, using the possibility to skip WLAN related packages: DietPi-Prep
Version/Date
Raspbian Lite: 2017-11-29
DietPi: 6.0 (without network access => no 1st run update to 6.1)
DietPi-Prep: 6.1 (with network access => all packages + DietPi up to date)
Download size [MB]
Raspbain Lite: 347
DietPi: 80,6
Image file size [MB]
Raspbian Lite: 1730
DietPi: 666
Root partition size [MB]
Raspbian Lite: 1046
DietPi: 445
DietPi-Prep: 387
- Raspbian Lite now offers automated file system expansion as well
- What is the reason, that raw image sizes are larger than the files, finally laid out on disk
Installed packages
Raspbian Lite: 439
DietPi: 247
DietPi-Prep: 232
Memory usage [MB]
Raspbian Lite: 32.3
DietPi: 27.1
DietPi-Prep: not comparable, access via SSH, active network and dietpi.txt 1st run preparation (headless, disabled HDMI), but was down to 24.3M after 1st run setup.
Active tasks
Raspbian Lite: 18
DietPi: 10
DietPi-Prep: 10+1 for active SSH session
Real performance measurements would be nice, I know, but I didn’t want to stress my actual production system too much and also wanted to bring it up as fast as possible. Horrible, to run 2 days without calendar sync 
.