The temp climb rate does not look normal.
But there is a factor I just found out about, by chance, yesterday: If your CPU supports AMD Cool & Quiet, it must first be enabled in the BIOS (it must also be supported by the motherboard). But this is not enough - you must also select the option "minimal power management" in:
"Start > Control Panel > Performance and Maintenance > Power Options".
I believe CPU fan control must also be enabled in the BIOS power tab.
The only place I have seen this written was in an ASUS motherboard manual. We also have a Gigabyte, and there is no mention of it. Of course, if you Google "Cool & quiet" + "minimal power management", you get 10000+ results - but this is working backwards, after you already know about it. My other Google searches trying to lower idle temps did not lead me to it.
As to the stock heatsink and fan: I have obtained decent results with the stock heatsinks for AMD Athlon XPs 2500+ & 2600+ (for the latter I bought 2 or 3 modestly priced HSFs that brought no improvement), and also for AMD Athlon 64 X2 6000+ (this is a 125 W CPU, it used to get to about 65 C after about 30 min of ORTHOS - 100% CPU usage; it now idles at 31-34 C vs. 40+ C before, and seems to stay stable in the 50+ Cs for about 10 minutes of ORTHOS - did not let it go further, for room temp about 30 C; after I discovered the "minimal power management" thing, of course; I did put in a 5000 RPM fan - stock was about 3000 RPM). I had built this system in january 2008 and it had idled at 40+ C, till yesterday. Good results also for Athlon 64 X2 4800+, it does not idle as cool as the 6000+, but still is at 38-41 C, and stable in the low 50s for the first few minutes of ORTHOS), for 30 C room temp. I did put the 6000+ stock CPU fan on it. Haven´t even changed the thermal paste. In short, fairly decent results with stock heatsinks, and modest fan changes. I do not overclock. Both PC cases are well ventilated.
For the little I have seen of the CPUs themselves, it doesn´t look like the heat spreader could be removed - but I am no expert.
If anyone doesn't know about the "minimal power management" setting, I would say this should be the starting point for any high idle temp issue.
Also, I don't think that Cool & Quiet works at the BIOS level
Excuse if these comment do not address your case directly, but I was surprised about how difficult it was for me to find out how to activate Cool & Quiet, despite it being such a basic feature in AMD processors. Good luck.