Maybe this could be of help. This does not cover all games producers, but still...
Playngo: up to 6 RTP Variants between 99% – 84%
Pragmatic Play: almost all games up to 5 RTP Variants between 96% – 87%.
Red Tiger: almost all games up to 5 RTP Variants between 98% – 90%
Nolimit City: almost all games 2 RTP Variants: 96% & 94%
Spinomenal: almost all games 4 RTP Variants 96% – 89%
Habanero: almost all games up to 4 RTP Variants between 98% – 92%
Swintt: almost all games 2 RTP Variants: 95% – 92%
isoftBet: almost all games 2 RTP Variants: 96% & 92%
Push Gaming: several games 2 RTP Variants: 96% & 95%
Netent: many games up to 8 RTP Variants between 99% – 90%
Microgaming: several games 3 RTP Variants: 96% – 92%
Blueprint: a few games 2 RTP Variants: 96% & 94%
Quickspin: a few Games 3 RTP Variants between 96% – 90%
Thunderkick: One game 2 RTP Variants: 96% & % 94%
ELK: Can't be adjusted
Yggdrasil: Can't be adjusted
That's a very interesting and accurate post but how did you find those figures? It's something you've found yourself by playing at different casinos, or it comes from private datas for professional only? It's very surprising to learn there are providers offering up to 8 RTP variants. I guessed it was 2 or 3 variants at most. You have no data for Evolution btw?