I also own a 745 and found out that it handles E2xxx,E4xxx and E6xxx 65nm 1033 cpus as you stated.
From digging around the web the E6700 is the fastest.
I have seen threads which says a Q6600 works but according to Intels website at this link: http://ark.intel.com/chipset.aspx?familyID=22756&wapkw=(q965)
the E6700 is the fastest.
Me personally I picked up an used $15 E4300 Allendale 1.8 ghz fsb 800 L2 2mb which I pinmodded to 2.4ghz 1066mhz L2 2mb which essentially equals a handicapped
E6600 Conroe (it has 4mb L2 and virtualisation Vt).
The pin mod is show here. http://www.overclock.net/intel-cpus/341123-intel-bsel-vid-mod-guide.html#post3980695
It is the only way to overclock a Dell/HP etc.
I dont recommend it unless your willing to risk your equipment.