The stock DV is not adequate for stock boost levels, they tend to leak and fail often, jsut ask your friendly VW or Audi techs how often they have to replace them. I have used the 06A 145 710N DV that some people are so crazy for and it began to stick, that valve is now sitting on a shelf.
Those composite valves like to fail for the following reasons:
1. The composite plastic material they are made of tends to change form at higher temperatures causing the diaphram to bind and/or leak.
2. The rubber diaphrams become weak and tear in a pretty short period of time and leak, this is caused by extreme temperatures, pressure and constant movement.
Many times they fail and you may not know it for awhile because they don't always "Honk" as a symptom of failure, they can stick open or closed or move slowly due to binding.
The Bailey, Forge, Turbo X style DV's whether ajustable or not are much better than the stock valves primarily because of the materials used to make them along with the fact that there is no rubber diaphram in them to fail.
The downside of these valves is that it is possible for charge pressure to push them open causing leakage, this is because the actual flow design is identical to the stock valve, with the exception of build materials and spring rate.
After using a number of different DV's, one of the main reasons that I finally decided to use the more difficult to install HKS SSQV is because it's design characteristics are completely different than the direct replacement upgrades.
The HKS SSQV is fully adjustable but the way the valving is arranged makes it so the charge pressure is actually pushing against the pressure release piston, the more boost pressure you feed it, the more the unit seals against leakage until de-acceleration or shifting accur.
The HKS SSQV also does away with that annoying part throttle fluttering making it much more predictable in it's operation, it doesn't just use spring tension to seal against leakage, the HKS SSQV doesn't open in the same direction that the pressure flows and this makes it a more responsive unit with far less chance of failure or leakage.