think globally, invest locally

this is not an one number game. You'd better use a matrix to measure.

Besides profitability, you cannot ignore liquidity and solvency. They are equally important.

to calculate profitability, you have to take all parameters into considerating, which include, but not limited to:

Property appreciation rate (or depreciation rate which could be more reasonable if treated like a consumable commodity)

Inflation rate

Mortgage interest

Rent yearly grow rate

Alternative investment return rate

......

Based on the current economic situation, 6% is ok provided that both liquidity and solvency are good. Otherwise, it's a headache because you cannot squeeze profitability anymore