One other issue, the KL processor had 72 bit wide floating point hardware, it was a fast number cruncher in its day (one reason the follow one Jupiter CPU faile

One other issue, the KL processor had 72 bit wide floating point hardware, it was a fast number cruncher in its day (one reason the follow one Jupiter CPU failed, it only had 36 bit wide FP hardware). The Pi Zero is ARMv6 and therefore has IEEE double precision 64 bit floating point, but move to the Pi 2 ARMv7 and you lose double precision in hardware....