That is the best comparison.
Just be sure to look at the actual numbers. Like all these sites, they want their charts to look dramatic and so they tend to exaggerate the distance between the bars on the charts.
The best thing I can tell you is, P45 is great for a single card or if you want to buy one card now, but keep your options open for a second one later, maybe.
If you are buying two cards right away and you want to crossfire for a monitor larger than 22" then you likely need an x48.