GPU shouldn't be increasing PCH temp.
Generally, that is a huge indicator of either lack of proper airflow in a case, poor airflow through the case (like having the front be an intake, back be an exhaust, so air gets trapped underneath the GPU), or that you need some directed air within the case (by another fan inside the case directing air to areas you need it).
My general experience, is when there are issues with heat, it's either a problem with the interface (ie the CPU/GPU/PCH and the heatsink, so bad compound or not tight enough, etc....) or poor airflow management within the case itself (ie bad airflow over components, or poor airflow in the case causing some components to not have enough airflow over their associated heatsinks).
If your top fans are exhaust, and front fans are intakes, it's very possible to have air flowing most in and out right away, without much air flowing to the back of the case to help the GPU, PCH, and VRM heatsinks, which would help explain your increased temperatures all around.
Personally, I prefer positive pressure inside my case. I want to push hot air out as much as possible. I have 8 intake fans, and 5 exhaust fans in my case (mine is actually a large cube, with a 2x3 arrangement of fans in the front). This means I'm pushing hot air out everywhere else the case has openings available as well, which means air is going to flow all over the case no matter what.
It's a different line of thinking.....and I can see why some would prefer negative pressure.....but I've found all too often it just doesn't work well unless it's specifically designed to do exactly that. Most cases I've found, just aren't.