485 will not be processed faster because of PP, but there is a chance that it will be slower if PP is not used. In other words, 485 will not be approved without 140, and if for some reason, your 140 gets stuck in the conventional way, then your 485 will not move forward without the 140 being approved. But this is towards the end of the 485 stage (where it doesn't move forward without the 140). The biggest variable black hole factor in 485 is FBI namecheck, and that can proceed without 140.
Apart from this, the peace of mind factor also points towards PP.
Thirdly, and I cannot confirm this, but it's only rumors that I've heard, but apparently the service centers are "irritated" by non PP 140s, and they have been slow to work on them of late. Don't worry too much about this, it's all hearsay, probably exaggearetd, but I'm letting you know FYI.
Now what you need to do is decide if the above three factors are worth spending $1000 for. The best thing is to get your company to foot the bill, then the decision is a no-brainer