I´m able to get 3.0 on a e4500 with slightly above vcore default (1.33), however, from that speed on, any slight increases in clock speed, require upping the vcore. Reaching 3.1, requires the vcore to be as close as 1.4, making 3.2 practically a mirage.
This happens regardless of the combination of multiplier x clock i use. I´ve been told that CPU PLL could be an issue here and tweaking this parameter (within certain limits) could be beneficial.
From a quick search, "CPU PLL" seems to be an ASUS BIOS parameter
According to Intel data sheets, you can push Vcore to 1.5 volts. Also, if you are using the stock HSF, a better one may help.
The following shows my OC settings (cut from an old thread):
I have an EP35-DS3P and Q6600 running at 3.6 GHz. Here's my settings:
CPU Clock Ratio [X9]
Clock Control [Enabled]
CPU Host Freq 
System Memory Mult [2.00]
DRAM Timing Select [Manual]
Memory Timing set to 4-4-4-12
System Voltage Control [Manual]
DDR2 Overvolt [+.40 v] Crucial memory specs
FSB Overvolt [+0.20 v]
MCH Overvolt [+0.100 v] Needed these two settings to run at 3.6 GHz
CPU Voltage [1.450 v] Droops to 1.40 volts
System is 24 hours Prime95 stable. With a TRUE HSF in an Antec 900 case, maximum load core temps are 65 C.
Running at 3.3 GHz, I need to set the CPU voltage to 1.30 volts. I can leave the FSB and MCH voltages stock.
Try boosting the FSB and MCH (or the P35C equivalents) a little.
I had the same idea regarding CPU PLL, that it was ASUS specific, just trying out my luck...
On what concerns my settings, they are very similar to yours and temps are not an issue, i think, since at 3.03 Ghz @ 1.36 vcore, they top 50º C after 3,4 hours of orthos stress test. Maybe they could be better, but with a Coolermaster Hyper TX2, i´m happy
I wouldn´t want to stretch the vcore far from where i am at this moment, as i plan on keeping the CPU for a while, it´s just a bit frustrating seeing people reaching much higher clocks with 1.36 on this CPU, but then again, i know not all components are the same...
In my research up to now, i´ve come across some statements that the more recent C2D E4500 don´t have the OC potential of the previous ones (mine is 4 months old). Maybe it´s just that or my mobo doesn´t have the OC potential i expected it to have...