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Is there any quality/performance differences between pistons that are flat and ones that are concave?

typically on these motors the flat top pistons have a higher compression ratio.
I say typically because it also would depend upon the chamber volume in the head.
Same head, flat tops have higher compression.
There are also dome topped 1.7 liter pistons.
You are showing dished and flat top.

Rich

Compression = Power

Dish = Lower Compression
Flat = High Compression
Dome = Higher Compression

If you can find domed, get em.