Hello. I am considering two different 2" memory foams to go over a fairly firm innerspring mattress. I will get them from the internet, so I really don't want to deal with the returns. One is 2.5 pounds, and 12 ILD. The other is 4 pounds and 10 ILD. From what I have read, the 4 pounds should be better quality than the 2.5 pounds, but the 12 ILD should be firmer than than the 10 ILD. I do not want the topper to be so plush that I push through the foam to the mattress. So, would I notice much of a difference between 12 and 10 ILD on 2" memory foam? Thanks

In my opinion, 2.5 lb memory foam is worthless. Provides no support. Go with the 4lb instead.
I prefer 5lb:
http://www.overstock.com/Home-Garden/Sensus-Memory-Foam-2-inch-Mattress-Topper/3657734/product.html