strap From what I can gather, the top 6 central defensive partnerships by games started is:
210 starts 1.48 ppg - Hicks/Wood
132 starts 1.45 ppg - Messer/Inglis
128 starts 1.33 ppg - Williams/McPherson
122 starts 1.73 ppg - Sonko/Ingimarsson
120 starts 1.72 ppg - Brice/Wicks
114 starts 1.60 ppg - Hicks/Hetzke
Can't find any others with 100 or more starts (should say that here I have treated loan spells as different from permanent).
Based in minimum 10 games started topgether, the best pairings have been
2.23 ppg from 13 starts - Upson/Williams
1.95 ppg from 20 starts - Shipperley/Hetzke (although Hetzke played RB for many of these games)
1.93 ppg from 14 starts - Whitbread/Viveash
1.91 ppg from 11 starts - Williams/Hunter
1.88 ppg from 42 starts - Williams/Wdowczky
1.83 ppg from 60 starts - Hetzke/Bennett
1.83 ppg from 29 starts - Barker/Lenarduzzi
1.79 ppg from 75 starts - Bennett/Hicks
1.78 ppg from 40 starts - Barker/Youlden
Hope this is of some interest!
So (unsurprisingly), given the number of starts combined with PPG, you essentiall have to go with Sonkomarsson. Especially seeign as they played at the highest level.
Although very impressed with the Hetzke/Bennett, Bennett/Hicks, Brice/Wicks & Hicks/Hetzke records