As someone who has been closely following the issue, my educated guess is that a high $1 CPM isn't necessary to initially qualify. .50 CPM would be plenty, and above that overkill in my opinion. However, there are some other variables, some we know and some we don't.

As you probably know, requalification to GS has been reported as low as around 34 CPM (cents per mile average over the entire year) and $40K spend, with at least three expensive ($4K to $10K) international business or first class tickets during the year seeming to be a must. Requalification requirement may take multiple year spend into account, so someone who is temporarily a bit low one year is still invited back if they show a pattern of high spend in the past year or two or four. We may be talking about such people when we quote this "bottom low" level. Maybe they had high spend last year or the year before.

To qualify for an initial invitation to GS, and again this is only an educated guess, perhaps as low as 45 CPM and $50K spend with at least four or five expensive international business class tickets. If you hit that level and they haven't contacted you already, you should at least point out your favorable stats and ask to be considered. Since it is believed that GS membership is allocated to the top 1% profitable customers in each market area, this level may qualify you if you live in, say, Moline but perhaps not enough if you live in San Francisco.