On my early 2008 20" iMac (in addition to 6MB RAM, and installing an SSD drive), I just upgraded the following:
Core 2 Duo E8335
SLAQC (C0)
2.67 GHz 6 MB 1066 MT/s 10×
44 W
Socket P April 2008
FF80576GH0776M
to
Core 2 Duo E8435
SLGEA (E0)
3.07 GHz 6 MB 1066 MT/s 11.5×
44 W
Socket P March 2009
AW80576GH0836M
Make sure to remove and add thermal paste.
Seems to work fine. They are the same size, use the same wattage, and same bus speed.