I was just curious to know what an A14 or other a series for that matter can rev reasonably safely to on a stock bottom end that is not balanced.

8000rpms, no problems.
They will hold together past that, but the flywheel bolt comeloose/break. (I've seen it first hand)
These motors are EXTREEMELY robust.
In order to pull real big revs, you need to replace the springs on the rockershaft with bushes. This prevents the rockerarms migrating down the shaft, and bending the push rods.
I knew a bloke who had a full race A12, it used to see 9500 all the time. Unfortunately with time the conrods will fatigue, (Or the big end bolts) and it spat a rod out through the block.
Any way, I show my supercharged A14 8000 whenever the need arises, and my bottom end is stock as.

It is difficult to say.
Alot of people here I have read can rev their A14 engines to 7000rpm with stock bottom end.
A12 I have'nt read of alot of people doing the same. I think Nissan did something when they changed to A14 to make it more of a balanced engine.
I have the A12 GX motor.
I have driven it hard quite a few times but cannot get it over my heart to take it past 6000rpm.
Between 5500 and 6000rpm it starts to vibrate and make a hell of alot of noise.
The GX double valve springs makes a redline of I think 6800 to 7000rpm.
I will NEVER take it that far.
It would definately drop a rod or vibrate something loose.

ive taken my A15 to 8500 easily..stock bottom end...ported head stock valves dbl springs twin 40's

i've put a rod thru the side of my A12 block at just over 6000rpm at 100mph under load in 4th gear.

so my guesstimate would be that 6000 in the lower gears should be the limit for an A12.

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Something else had to have been wrong.
I have abused stock engines badly enough to make most people cringe, with EVER suffering rod failure.

With the cam i've got I change just between 6500 and 7000rpm because thats the power band and i feel pretty safe there with all the stories of people hitting 8000rpm without any trouble. My uncle who is a mechanic rekons that the A series have an almost unbreakable bottom end and I would believe that after pulling two down and seeing the thickness of the crank and rods for such a small motor.

edit: Also my uncle just built a supercharged a15 for this bloke who sent away to america for forged pistons and rods + the crank was shot peened and to date he has run a 12.8 quater on this engine at over 9000rpm

If anyone really wants to know I could get the profile of his head that my cousin ported.

how much would it cost to supercharge an a15...cheaper then a sr20 conversion? just wondering cause i have a 1200 ute and am looking at sum different options...12s in the quater is what im looking for...

looking back i really should have inspected what was wrong and why it happened, i was just shocked when i opened the engine up (it was rooted btw) and all the bolts had been oversized by about 1.0mm and and ARP stud kit run thru the bottom end, with what looked like linished rods. i was really quite stumped considering it was a student's car before i owned it.

i know a wrist pin let go after the piston craked around that area, but i really wish i had looked further into it now.

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the A12/14/15 have 5 main journals, but the A10 only has 3 - god knows how these little things stayed together with their racing history.

i wanted to sling an A12 crank and rods into an A10 block with a "head spacer" like the OS Giken 3L stroker kit for the RB26, but looks like that idea's been binned now!