Yz or kx 125 or 250 power?

OK. I am on the search for a dirtbike. My brother in law has a yz 250f. My friend has a yz 250. I am looking to buy one. I have a sharp budget so around 1500. I found one yz 250 and a couple yz and kx 125. To keep up with them I think the 125 could with 250f but what about the 250. If not how much power defference is there.