Hi and welcome to PCHF!
You should be fine upgrading to either one as you said.
Supports Athlon 64 X2
CPU: 3800+, 4000+, 4200, 4400+, 4600+, 4800+, 5000+, 5200+
If you don't know how to do it, I would recommend having an expert doing it as your CPU is a VERY delicate and essential piece of your computer. You will need to make sure the heatsink and other components and materials are done exact or you will have overheating or other issues.
Otherwise, I would recommend the first one, the AMD Athlon 64 X2 6000+. My reasons for that are it is much cheaper and the more expensive one is only better by 200 MHz (.2 GHz) and that is not enough in my opinion. Also, from the more expensive one, it says "
NOTE - This product is not supplied with a heatsink & fan." and that scares me. You would also need to find the right heatsink and fan for the
CPU.
Hope this helps,
Adam