Maybe it's not precisely what you ask for, but it's quite interesting:
Track I've made comparisons on is Brands Hatch GP. It was rebuilt after 2002 (Dingle Dells/Sheene's corners), though I don't know really how much it affected the speed.
According to:
BTCC 2000:
http://www.touringcars.net/results/2000/qual1.php
BTCC 2010:
http://www.btcc.net/html/raceresults...0&season_id=53
WTCC 2010:
http://www.fiawtcc.com/events?idSeason=19&idEvent=87
In 2000, on the old track, the ST's from BTCC, pole time was 1:27.9, with the top Honda Accord doing 1:28.5.
For BTCC 2010 on the modified track the pole time was 1:31.6 while top Honda had 1:32.0.
It was Civic S2000, though perhaps the specs have evolved through time and possible differenced from BTCC/WTCC rulesets.
WTCC 2010's pole time was 1:32.4.
Though the question of the modifications makes the comparison difficult, I believe that ST's were about 1,5-2 seconds faster on that circuit.