Most of those races wouldn’t come close to the Derby in terms of tote turnover.
They publish the figures each year around this time in the Racing Post (or is it the end of the tote’s financial year?). You could wait for that or wait for the tote to reply to an e-mail enquiry from you. The latter would probably take forever.
Group One races are much higher turnover on the tote these days than big handicaps due to co-mingling.
The hierarchy probably looks something like this
1. Derby
2. Ascot Gold Cup
3. Other Royal Ascot Group Ones
4 Other Royal Ascot Thurday races
5 Royal Ascot races outside Thurdsay
6 Other Epsom Group Ones
7 Other Derby Day races
8 Other Group Ones
York Ebor meeting is probably best of the rest, followed by Glorious Goodwood.