It's generally not an issue. I used to use way too much putty and still get decent results. Laptops are where you don't want to overuse it, so don't buy more then 20g when doing a laptop.
You can also use my Putty Calculator of you like. That's if you measure the stock pads thickness, width...
You can expect to see 30-40 Celsius on your VRAM with top end putty and a water block. But I believe you'll want to keep them closer to 55-60 Celsius since you have 2GB VRAM chips which don't overclock as far at cooler temps.
70 Celsius is honestly fine for them. If you do get a putty for then...
You can definitely get some decent gains. Lots of folks in my Discord with 7900XTX's on Putty and PTM.
There are quite a few good putties already on the market (HT10000, UTP-8, LTP81). I have yet to test these Thermal Grizzly putties. Will do it as soon as I can.