When using Thorograph's Sire Profile at what point does a handicapper use an entry based on today's surface? Is it two points faster, three, four?

I understand current form and cycle is important as is the mare and foals data (in the upper right hand corner) but at what point would one be inclined to use a entrant in decent form on a surface switch? There are sires I always gravitate towards for grass based on these numbers with good results but wondered if anyone else had a threshold they used.

Thanks for your responses.