cards has the higher ceiling probably but you end up working for it more; i'll make close to 600k this year from rvu goal/group bonus/quality metrics.
most days are packed; reading echoes, stresses, ekgs, holters, nukes, clinic, rounding.
heme/onc probably more chill but also 1 cms change away from being 400k to 200k if chemo billing changes.
that said, cancer and cards both keep hospitals afloat, so likely salary would be subsidized from downstream revenue if there were major reimbursement changes (eg no cards = no cv surgery = no hospital; onc is likely similar with surgery, infusions, radiology, halo effect, etc). cards has had **** cut a bunch in the past 10 years and everyone in the community still makes >500k.