Hardware differences between test models and final release??

Wondering if there are any hardware differences between the M8's that were released as test devices and the final product that meizu released to the public??
I know that the WIFI chip is one difference, but are there any others?
Could this be a reason for the performance of the device versus the firmware build??

Im wondering cause i have an M8 that was aquired in late 2008.

And the firmware builds keep giving me worse and worse useability.

It is possible that there are differences,
most companies do on revision of hardware while doing the production itself.
Only way you could ever know is by opening a bulk of m8 devices ... or requesting it on meizu and hoping they answer the truth.