If like me you've been suckered into replacing a more than worthy Nvidia Geforce TI4200 with a sub par Geforce 6200 AGP (N44 / N44A) you'll want to know why you (may) not be able to overclock (or underclock) the core speed, even by just 1mhz, memory overlocking is fine.
I bought the card because games like Matrix Path of Neo required Geforce 5x00 and upwards features, according to reviews such as this one for the XFX 6200 AGP, its an average piece of kit. Unfortunately XFX decided to create multiple versions of this card (including low profile versions) one of which was far slower - so slow it is quite frankly almost unusable imho.
When I got the card I found I had a low profile version, with a core of 350mhz as documented in the review but its memory clock was a lousy 400mhz (on an already poor 64 bit bus) and not the 500mhz the review mentioned.
All was not lost, by overclocking this card getting around the buggy 81.40+ (core locked drivers?) I was actually able to get an acceptable performance with very little extra heat which is good since the card has a passive heatsink (no fan).
I'll be documenting this process here later.