P.S. I was going to suggest level 5, but whatever. [
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I'm cool with that
, epecially since I can trigger encore with it (and you wouldn't without leaving CB un-upgraded). Really though, there's multiple points to speedruns, and multiple objectives.Take your pick, and we can agree on whether that's worth doing or not.
I did not know this triggers encore. Very interesting... 
Since you didn't know about the encore feature, you've been doing worse without it. Have fun using it. You need to incorporate killer set encores consciously into your playstyle, weaving them in between magical songs.
It should make PC easier since you claim you're having difficulty getting encore with PC. FB (or any magical song) --> killer set boosted basic attack (either kills and triggers encore or weakens) --> PC (kill and encore, or weaken enemies) --> basic attack or PC for another encore --> repeat.
The real point of showing off is the demonstration of skills involved by players that know how. Presumably that you're better at CB than I am, and vice versa with PC. Since I would be using the encores from killer set basic attacks in between PC as needed, I can produce a lot more PC than you previously imagined (even if PC fails to trigger encore, killer set would not)
Of course you have to balance between how much mana you have, and if you think your next song will finish the enemy vs slowing down for a killer set finish vs running to/away from an enemy. It is an intense thrill-ride weaving in and out of enemy range, watching mana, space control and damage.
I could cold beats kite as you do, and I have as needed, but I find I can PC and killer set encore as needed for the most part. This discovery is something everyone learning virutoso needs to learn. I did put it down as a footnote in my build guides, but its not like everyone reads those thoroughly.
Edit. P.S. I still do want data on how often PC misses encore on XB1.