New to GC Estimating - Production Rates, Equipment Rates & Assembly Libraries Question

I’m relatively new to GC estimating, although I have several years of experience preparing detailed subcontractor estimates.

On the subcontractor side, I’m used to estimating from a historical cost database and building assemblies around known labor production rates and man-hours from previous projects. As I transition into GC estimating, I’m curious how other estimators establish their labor production rates and equipment rates, especially when they don’t yet have much company-specific historical data.

I know RSMeans can sometimes be viewed skeptically in the construction industry, but for a GC that is just starting to build its estimating database, is it reasonable to rely on third-party production and cost data as a starting point and then refine those rates with actual project performance?

If so, what third-party resources have you found to be the most reliable for production rates, equipment rates, and general estimating benchmarks?

Also, does anyone have a GC estimating assembly library or sample database they would be willing to share? I’m mainly looking for something to use as a starting framework while we develop our own historical data.