I recently bought a FORSA 256MB 6200 with the NV44 A1 core. For about two weeks I tried to push my card to see how far it can go. Here's what I've learn't
Firstly, since its an NV44(and you've already found this out yourself), there are no extra pipelines to unlock.
Secondly, the core is locked(aka the com hangs when you use the coolbits hack), so you cant overclock the GPU or the memory without some tweaks. Initally, I overclocked by copying, modyfying and then flashing the graphics bios. It was a bit tedious, but at that time thats the only way i knew(I wouldn't recommend it if you're a casual overclocker. I messed up a few times and had to blind flash the card). Luckily after all the modding, the GC isn't seriously damaged.
Later on, I found out that the latest modified forceware driver by
TweaksRus unlocked the core, and thus the coolbits hack could be used(the modified driver automatically installs the coolbits registry string). I'd suggest this method as its much more easier and all mistakes are reversible.
TweaksRus
Now, before you start doin anything, I'd like to warn you, if you're not willing to spend the time doing this, don't bother.
The big heatsink provided with my GC came with a small fan, and thus is one up than yours. Also, even after putting in a bigger fan(I glued one of the casing fans on the heatsing-it ran about 5 degrees cooler), I could not overclock much. The core becomes unstable soon, and the memory chips I got couldn't even be run at their supposed speed(i checked the serial no of the chips on the websites and they were rated for DDR2 667, but it was unstable after about 630 MHz DDR(ie 315Mhz). Needless to say, benchmark performance increase was minimal.
If you want to put a fan, my advice would be to put one of those old pentium 2/3 fans. The lead on my GC wasn't the three pin one, so when I tried this I connected it to the spare chasis fan lead on the motherboard. Do secure the fan properly, as the vibration can loosen it.
As for my overclocking result i managed a stable 420 core(from 375) and 630 memory(from 532 - halve that if you're considering the base frequency because its DDR). The max I went was 460-670 but it became unstable if the load on it is high(ie when playing games).
The last thing I wanna add is that after the two weeks, when I reverted the settings back to normal, the system became sluggish. Games that played smoothly before started lagging, and did so even after i reduced the game setting to the lowest possible settings. I doubt its a hardware problem( mayb reinstalling Windows would help, but I havent tried it yet).
Hope that helps. HAPPY TWEAKING!