The TPG's use 4-7x magnification for initial grading and only go to the big guns if there is anything major to look for. You should be able to see RPM's easily enough with your 4 x glass. a 30x Loupe, which are pretty cheap these days will help if you're looking for Doubled Dies etc
I'm watching for them too.i don't pay much attention to double dies.i read lots of comments here,these lincoln pennies are cool.i bought these knowing nothing .still learning.
After searching about 2 tons of pennies 5 years ago I have about 50 pounds of wheats. Someday I’ll separate them by year and search for doubled dies. Someday I may run for Congress. Someday
I use a 4X loupe. It is plenty when looking for RPM's even most DD's. No need to go past a 10X. You will start seeing things that really are not there. Here is a good reference page for rpm's and Doubled dies. http://varietyvista.com/index.htm