Your E5450 Xeon cpu is similar to the Q9650 cpu and overclocking to 3.80 - 4.0GHz shouldn't be a problem.
You will need to increase Cpu Vcore as you o/c higher.
You might need to set:
FSB OverVoltage Control___ [+0.2V]
(G)MCH OverVoltage Control [+0.2V]
I recommend that your set:
PCI Express Frequency (Mhz)_______  <-- 100 should also be OK
After my systems had passed extended stress testing, my P35-DS3L and P35-DS4 systems passed additional stress testing with:
Performance Enhance = [Turbo]
CPU Enhanced Halt (C1E) _____: [Enabled]
CPU EIST__________________: [Enabled]
Static tRead Value = 7 is stable with 8GB of memory on my P35-DS3L system with CPU Host Frequency = 438MHz. YMMV
Memset v4.1 will show this value as Performance Level. Memset v4.1 Download - Tweakers.fr
I don't think that C2/C2E and C4/C4E State Support was available on my systems.
My Q9650 booted and passed minimal stress testing on my P35-DS4 system using 9 x 460MHz = 4.14GHz but cpu core voltage was too high.
The Q9650 is currently running at 9 x 438MHz = 3.816GHz and passed all of my stress testing.
9 x 445MHz = 4.00GHz was also stable but I wanted to use somewhat lower cpu core voltages.
My P35-DS4 + Q9650 + 8GB Mesmset values are similar.