Emulation certainly does have a lot to do with processing power but that's just one piece of the pie
The xbox1 has had sooo much love and attention over the years that it is still (IMHO) better than emulation on xbox 360. I use both, but mainly the xbox1.
For arcade you want to check out FBL. (Better than MAME on 360 I think)http://www.underground-gamer.com/details.php?id=54373
That is v1.7 with a complete rom list. FBL is currently at v1.9, you'll find 1.8 and 1.9 updates at xbins!
And talking about super nintendo emulator Zsnes. Maybe you should check this out! It's the newest version of snes9xbox (even comes with a separate apu core for sink or swim!). It's certainly worth check out http://www.emuxtras.net/forum/viewtopic.php?f=183&t=1714
One day the 360 might take over where the xbox1 left off. Especially since RGH is now so available (unlike jtag)
Hope this helps a bit mate!