Now, the Core 2 Duo exists in the following versions (sorted by performance):
The energy need of the processors is marked by pre-set letters in front of the type designation (number).
X ... Extreme (fastest) version with the highest current consumption
E ... >= 55 Watt (Desktop PCs)
T ... 30-39 Watt (Standard laptop CPUs)
P ... max 25 Watt
L ... 12-19 Watt (Low Voltage)
U ... <11.9 Watt (Ultra Low Voltage)
The 4-digit sequence indicates the type series (first digit) and performance (other digits). The Core 2 mobile processors ought to get 5XXX and 7XXX (at present T2XXX for Core Duo and T1XXX for Core Solo).