For my setup I use VB Cable with any RTL dongle with SDR Sharp and PDW 3.1 and it works perfect. I don't know if it has anything to do with the difference between VAC and VB Cable but it works great.
I've no idea what the differences are but I do know that on one PC I use VAC and on the other VB Cable. Always used VAC in the past but it won't play ball on this particular PC.
To confuse matters further, both PCs use the same processor, have the same version of windows, same make and quantity of RAM, same motherboard, Same SSD/hardrive combo......
So the one on which VAC works has a lot of 'cables' and this one has three. No problems with either in terms of their working but VAC certainly a bit more effort to set up than VB Cable initially.
Back to PDW and it's meter.
On one flex freq I rarely see the meter show more than 5% yet it's giving me 100% good decodes and doesn't appear to be missing any pages - I guess the poor percentage figure is because it's also trying to decode 'noise' and failing.
On a quieter flex freq I constantly get 100% but the actual decodes will vary from being perfect to being almost totally garbled (whilst still showing 100% on the meter).
...so I pay no attention to the meter or the triangle/percentage decode