I would second on that one. The Herc doesn't seem to overclock very well at all. I've seen cards with std memory that performes better than their 5.5ns memory.
Now. The Gainward Cardexpert Golden Sample. Now that's an overclockable card. It's got Elite 5.5ns memory. I have mine at 215/250 core/mem.
Yes I did apply some additional cooling on both RAM and core, but I've also read it's possible to reach those speeds without extra cooling.
Here's a link. It's german, but you'll get the point. http://www.chip.de/PC2D/PC2DB/PC2DBA/pc2dba.htm?id=667
Good luck on your buy.
Boy am I full of it - in every respect.