Mac Pro 3.1 Nvidia 8800GT problem

Here I am again guys

and after about 3,5 months from 8800GT failure and rebaking it succesfully, the card is dead again, so I baked it once more.

I am on OSX Yosemite 10.10.2 now with my Mac Pro 3.1. I don't use photoshop or any 3d game.Beyond safari, firefox, mail, youtube, itunes and some other common apps, I use Wmware for win7 and xp compatibility and there I have installed Autocad 12 but I don't use it for 3d design. I do some movie format conversions with Handbreak (6-10mins job) every now and then. Recently, last 15days, I started to use Garageband and a little imovie 2-3 hours a day both of them. I understand that, this is not heavy duty jobs for the graphic card!!!

What's surprising me is that MacPro works without the card installed!!! via Teamviewer.

I have made a few secs mov conversion to mp4 format with Handbreak and also played a few secs movie with quicktime, I am afraid to use the mac for a long while because I don't know it's capabilities in this situation and I don't want to have a severe damage.

I've always noticed that Handbreak was taking all the cpu juice when doing convertions although I thought that the GPU does the major job for that. But then, when the GPU gets working? Only when sending picture to displays? I don't think so...

So question 1 is: when the graphics card get's into play....and get stressed by my Mac?

and question 2: I am planning to buy a low budget nvidia card for pc -non EFI so no Boot screen- and install it as a main card.

I am thinking to replace my 8800GT with this Asus gt740

http://www.asus.com/Graphics_Cards/GT7402GD3/overview/

or

http://www.amazon.co.uk/gp/product/B...A3P5ROKL5A1OLE

Then install again the rebaked 8800GT and leave it unconnected to screen. I will connect it to a screen only when I 'll need the boot screen, or update OS. Will this combination make the 8800GT to stress and overheat as before?

question 3: I use the term overheat just because the card fails, I don't know a way to measure the card's temperature and I pretty much like to, just to see what's happenning to card under any jobs..