You don't remove the "original thermal pads" just like you don't remove the stock cooler because it is "old" ... you remove and replace it because you want something better than the cheap stuff the component originally came with. Here are some instances where you would want to change thermal pads ....
a) They were never installed ... EVGA 1060 - 1080 SC and FTWs for example.
b) You are swapping out cooler for a water block
c) Your VRM temps are higher than shown in reviews (adjusted for ambients) and perhaps you have a poor mount due to a crease in pad or other reasons
d) You want to improve cooling versus the cheap / crappy pads that were installed at the factory
We use Fijipoly pads ... they come in many sizes, we usually buy sheets and cut to fit. Often tough to find out the actual thickness and when taking off the originals that have been under 40-70 pounds of pressure, they may not recover full thickness. Consulting water block manufacturers instructions is a good source of info.
What is "better" is eveidence by the heat transfer rate, the more heat they move, the better. They (Fujipoly's) come in various performance quality levels:
Thermal Conductivity 6.0 W/mK
Thermal Conductivity 11.0 W/mK
Thermal Conductivity 17.0 W/mK
Other manufacturers sell pads as low as 6.0 W/mK which is probably what you get from the factory.
Good info here:
Welcome to FrozenCPU, support PC builders since 1999. Check out the latest and greatest PC water and air cooling components for your next build. EKWB, Mayhems, Aquacomputer, Watercool HEATKILLER, Bitspower, and more. We offer same day shipping, rewards with cash back for your next purchase, and...
www.frozencpu.com
The Thermal Grizzly Pads are only 8.0 W/mK