External recorders do usually improve the compression rate, but they cannot change frame rate/resolution. You won’t be able to get the 60fps in 1080p.
While an external recorder will probably be a little cleaner, you will not see any noticeable improvements on the 7D. Even on the 7D Mark ii, the HDMI out only gets 8 bit, which is what you get in-body in both the mark ii and the mark 1.
As I’m assuming this is your A cam, with your max resolution being 1080p, I’d feel safe using the 60fps slow motion if you need it. It’s noticeable to tech nerds like us, but for the most part you’ll be fine.