The amount of torque and horsepower your engine is making will also be a point of consideration here...as greater torque produces more acceleration forces on the crank as it turns around to change direction.....i see a rod bolt being the one to let go, then again, they did skinny the 7 bolt rods down.......anyones guess here, i wouldnt be going a nay past 8 grand.
Another point, a failed bottom end due to rpm usually sees a snapped or buckled rod...a snapped or buckled rod usually exits the block, a block that's had a rod through it always has a hole in it, a block with a hole in it goes in the recycling bin..the point of the story is that if you play with fire, youll risk getting burned, and in this case, its an expensive burn.
Its a true but unfortunate fact that not much can be done on the cheap, and sometimes a forged setup is required.