Evaluating broadband RF mixer?

There are many broadband RF mixer MMIC , But their datasheet always give characteristic under specific condition, typical a narrow band application. How to evaluate the performance under broadband condition? Or what margin should be when design broadband RF converting link?
For example ,IF a mixer?s IIP3 is 20dBm at 900MHz RFin, 70MHz IF out, what IIP3 could be expect at 0.1~3GHz RFin, and 70MHz IFout?

Out of the mixer band, the IF output signal maybe have spurs so that you can't use it. It's not only the IP3 problem,

May be the most modern answer to your question is: USE X-PARAMETERS !