Brent Spiner is 1.778 m tall. I will take unnamed E-E crewman as being of same height. Diameter of fuel part of GCS warp core is 0.71 m and SCS warp core has 7 tubes each having diameter of 0.4445 m. Thus we have crossections as following:
GCS: 3959 cm^2
SCS: 7 x 1551.79 cm^2 = 10863 cm^2
From that, I would guess 8.78 billion GW as standard power output of SCS warp core. However, standard power requirements of Sovereign class are probably smaller than GCS due to SCS being smaller, so take that guess with lot of salt. Either way, maximum power output of SCS is certainly higher than that of GCS, as much as 2.7 times greater.