i have to agree with the internal and external clock mention
also, from my experience of OC'ing GPu's, there is a limit, then they literally hertz themselves apart. I took a GeForce 610 from 810(stock) to 1100 mhz, it really didnt enjoy that, infact, the whole screen went purple and i had to wait an hour for it to cool down and reset, with the power off
(after adjusting the fan control, replacing the heat sink and talking to the card, it now runs stable at 1300, the max for the card i think, but i generally find it works fine at 1013mhz (as close to 1ghz as i can get))
that brings me to a point.. what's the difference for 400mhz when you've already taken 30 mins off? i'd be happy with that, i run a gaming rig on a 1.013GHz card and 3.5GHz cpu, using only mild overclocks (203 for gpu, 500mhz for cpu) and it runs perfectly, it stays cold, loads fast and never crashes, ever. It can process a 5GB video twice in just under an hour at 1080P. It's got 16GB of ram.
My laptop is the same, the graphics are internal, but i still raised it by 100mhz, perfectly safely, the CPU is an i5-3230M rated at 2.6 GHz, that runs perfectly well at 3.3Ghz, but also idles over at 1.17 on demand. I set it up so "balanced" power mode is 1.17GHz standard and it raises it if needed, but also resets the GPU clock, and "High Performance" brings it up to 3.3GHz and raises the gpu. Perfectly stable.
I would personally keep your stable 4.6 and maybe look into some better coolant, have a look at the bus speeds too and, if you do raise them, once again a little at a time
but, if you want to go higher, i would go with caution, increase 100mhz at a time and look for instability in the system, that way, you've got a chance of spotting it rather than going straight to 5 and melting the whole universe
