720 unlocked and overclocked :)

hey everyone, just wondering how wise it is to overclock a 720be after you have unlocked the 4th core? when it was a tri core i had it at 3.8 with the voltage slightly upped, how wise is it to up the voltage though after unlocking the 4th core? i got it stable at 3.4 at the minute very happy, especially as gigabyte have just sent me a GA-MA790GP-UD4H in replacement of my ga-ma790fx-dq6 very happy, its a great board!
so yeah, if is it safe to up the voltage on this puppy? i got no way of checking the temps, but i can tell you that idle it is 40 degrees, thats checked in bios, i have zalman 9700 aftermarket cooling,
system specs

720 be unlocked to 4 cores overclocked to 3.4 stable

xfx hd4890 overclocked to 915 on the core clock and 1200 on the memory

zalman aftermarket cooling 9700

GA-MA790GP-UD4H motherboard

antec truepower 550

grr!!!, well ive been running 3d mark all day, and been playing crysis for around 3-4 hours, i presume this is enough to ensure stability? im not really fussed about upping it any further really, one thing i am trying to work out though, whats better? 4 cores at 3.4 gig? or 3 at 3.8? i know obviously 4 at 3.4 has more processing power, but 3 at 3.8 i get higher scores on 3d mark etc... confused

1. 4 cores at 3.4 GHz is better than 3 cores at 3.8 GHz for running most applications and multi-threaded applications. Games aren't quite there yet. 4 x 3.4 = 13.6 GHz, 3 x 3.8 = 11.4 GHz.

2. You'll get faster 3d mark benchmarks because of your higher frequency. Having a 4th core over 3 cores doesn't benefit that much more even if it was at the same frequency.

Note: This is just my assumption from what I've studied, but anyone that's more technical in details could give you a better answer.

You CAN'T add the speeds of each core.