Please read: G-250, G-200, G-200 Balanced, R-190, R-108, R-109, R-156 and others.
The G-250 and G-250 V are essentially the same reg with the above mentioned orifice difference "G-250 V has a plastic orifice and the G-250 has a metal " and cosmetic changes.
1 ) If the orifice is even slightly damaged or excessively worn in one of the following regulators (G-250, G-200, G-200 Balanced, R-190, R-108, R-109, R-156 and others.) Inhalation effort is compromised as more spring pressure is needed to stop any free flow.
2) An older stiffer diaphragm will cause hard breathing in the following regulators: G-250, G-250V, G-250HP, G-200, G-200 Balanced, R-190, R-108, R-109, R-156 and others. The problem is often cured with a new diaphragm if a new orifice did not resolve the issue.
There are also minor differences in flow vanes:
3) With the G-250's and you can reverse the flow vane, so it is possible to have an identical inhalation effort with a difference in the VIVA effect even with both set at "max".
Personally, I have 5 or 6 G-250's and all deliver a cracking effort of less than .8". In the water you need about 1.0" to prevent a slight free flow between breathes so the extra .2" of performance is a moot point.
In comparison to a X-650:
4) The G-250 or G-250 V will breathe better with a lower usable inhalation effort due to better case geometry and the G-250 / G-250 V will have less dry mouth due to the metal air barrel.