Think you're overestimating the size of Premier League grounds: Bramall Lane would be 10th biggest in the Premier League this season. There are a further 7 bigger grounds in the Championship.
I'd say that anything over 30k is Premier League then anything over 20k is Championship.
Premiership grounds bigger than BDTBL:
Old Trafford 75,600
White Hart Lane (rebuilt) 61,000
Emirates 60,250
Taxpayers' Olympic Stadium 60,000
Etihad 55,000
Anfield 54,000
St James's Park 52,500
Stamford Bridge 41,750
Goodison 39,500
Premiership grounds smaller than BDTBL
St Mary's 32,500
King Power (Leicester) 32,300
Amex (Brighton) 30,300
Bet365 (Stoke) 27,700
Hawthorns 26,850
Selhurst Park 25,100
Kirklees Stadium (Huddersfield) 24,500
Vicarage Road 21,400
Turf Moor 21,400
Liberty Stadium (Swansea) 20,900
(Bournemouth) 11,500
Championship grounds bigger than BDTBL:
Stadium of Light 48,700
Villa Park 42,700
Hillsborough 39,700* (currently reduced to 33,800 on safety grounds)
Elland Road 37,900
Riverside 35,000
Pride Park 33,600
Cardiff City Stadium 33,300