Would PCI exhaust fan work against case cooling?

I suggest you look at the airflow paths in the case.

Typically it will be hotter at the top of the case & easier to push/blow hot air OUT at the top and pull/suck cold air IN at the bottom.

There will be a fan in your Power Supply .. most blow 'out', so air will be flowing towards the power supply (if your PSU is at the top, all well and good).

Next is the CPU fan - most will 'suck' air upwards away from the chip ...SOME have ducting that directs the hot air to a 'vent' that sends it straight out of the case = this is ideal because there is no reason to want that hot air 'circulating' inside the case just getting hotter & hotter ..

Then there is your case fan ... IF it's at the top, blowing out is fine .. IF it's at the bottom you should reverse it to suck in (but watch out for it picking up dust from the floor).

Now to the graphics card ... plainly the trick here is to get more airflow .. so removing any PCI slot case covers above (lets hot air out) and below (lets cold air in) the card would be a good idea.

Finally have a look at your case design = are there any cover plates that could be removed to improve air flow and/or could you fit another fan anywhere (often there are air slots in the bottom of the case below the disk drives .. on some cases there may be enough room to fit small fans sucking air in )

If the CPU fan just circulates hot air, you could also look to see if it's possible to add 'ducting' to direct the hot air straight out of the case (eg via unused PCI slots or through the front eg via an unused hard drive slot - or even through new holes drilled into the case side panel directly above the CPU fan)

If the case fan is sucking air in, can you add ducting to blow some of that air over the graphics card ??

If all else fails you may have to drill or cut vent holes in the case (and add your own fan), or simply replace the case with a bigger one with more vents and more fans ..

FYI = I've used 'square section' plastic drain pipe 'footer' as 'ducting' on overclocked CPU fans with great success, directing the air straight out of the back, via a hole cut in the case (above the USB / video etc. connectors)

It will work, however what you should do is download & install CoreTemp. Then you can monitor the actual temps. instead of just guessing.