I looked into this a little while ago in another topic, comparing it to a Raspberry Pi 3B+ (see How powerful is the Librem 5, and how could I make games for it?)
CPU:
Nokia 920: 2x Qualcomm Krait cores running at 1.5 GHz, which get a rating of 3.4 DMIPS/MHz (according to https://en.wikipedia.org/wiki/Comparison_of_ARMv7-A_cores)
Librem 5: 2 or 4x Cortex-A53 cores (depending on whether we get an i.MX8M dual or quad), also running at 1.5 GHz and which have a DMIPS/MHz rating of 2.24 (https://en.wikipedia.org/wiki/Comparison_of_ARMv8-A_cores).
This appears to be about 0.75x the per-core speed of the Nokia 920 and is actually quite interesting, as the two wikipedia entries I checked actually rate the older ARMv7-A cores as faster on an instructions-per-clock basis than the newer ARMv8 architecture.
EDIT: duh, got the numbers backwards.
(no, I don’t know how comparable this DMIPS/MHz number is, but it’s the first appropriate-looking thing I could find on the wiki)
Graphics:
Nokia 920: Adreno 225 = 0.8 GPixel/sec
Librem 5: Vivante GC7000Lite = 3.2 GPixel/sec (4x better)