I'd recommend trying for 21st Century Breakdown as soon as possible. For me at least, that was the hardest song on bass.
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Guitar Hero + Rock Band Expert Drums Dual FSFC - September 21st, 2017
10,000 unique expert GH/RB FCs - May 18th, 2022
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http://www.YouTube.com/dayzeed
FC spreadsheet:
https://bit.ly/FCs
Proud lefty who conformed to right-handed mode... show some respect! ;)