A litlle blast from the past - overclocking an i3 540

[The Coolest]

So I have had this i3 540 on the MSI H55M-ED55 for more than 8 years now. I always ran it at stock frequency (I did OC the iGPU for a while at the beginning)
I decided to play a little bit with it and see how far I can push it. The current setup is:
i3 540, MSI H55M-ED55 on the latest (1.7) BIOS, 4x2GB DDR3-1600 G.Skill RipJaws RAM, Antec 380W PSU (Antec NSK2400 case), cooled by Arctic Freezer 7 Pro rev2 with AS5 as TIM, so temps are under control.

I was able to clock it up to 4GHz without breaking any sweat, it even passed about 2 hours of linpack, and seems generally stable. But anything over that magic number feels like I'm hitting a brick wall.
The mobo seems a bit finicky with high bclk and changing things like the memory multiplier or QPI multiplier, causes it to fail POST. After saving the settings it reboots, restarts a couple of times and POSTs with an error that the overclock has failed.
Vcore is at ~+0.200v for about 1.3v, all the other voltages are at stock. Currently I have the XMP memory profile enabled, and so the memory is overclocked too. Changing the memory multiplier down to x4 fails POST sometimes, others it doesn't have any effect.

I tried dropping the multiplier to see how high I can get bclk to go, to no avail. I have the iGPU underclocked, and I keep it at around or below 700MHz.
I tried playing with VTT and PCH voltages, but it didn't do much of anything in getting this board much if at all past 180MHz bclk. I can get it to boot in steps, going from 174 to 180 then to 185, but if I change anything else it just refuses to POST.

I know that this platform is ancient by today's standard, and 4Ghz is a 30% overclock, which is more than decent. But it's apparent that this chip can do more, maybe much more, but the motherboard or some tweaks I'm missing are keeping it back.
I'd appreciate any advice on how to push it a little bit further.

[Charles Wirth]

So long ago already, did you see any high bclks on this mobo on the bot? I would suspect it is the limiting factor.

[The Coolest]

Yep. I think I have had it for over 8 years now.
Recently started using it as a Linux build machine. So I thought that a little bit extra oomph without spending much $ on upgrades of ancient h/w would be fun.
Not a very popular board on the bot. Looks like there's just one entry of a i5 655K, surprisingly at the same exact bclk (174). I think that 4GHz is a decent O/C, just looks like the chip is capable of more.

I read a review where they managed to get it way past 200Mhz bclk, but maybe it was just the luck of the draw.

[The Coolest]

Here's the review I was looking for: https://www.tomshardware.com/reviews...d,2555-21.html