Recently I started mining, and after about 3-5 mins of using CGminer (or anything else that uses cgminer, like 50miner and guiminer) I reach 100% CPU load. When this happens my Hashes go down to 300k/h. Any fix?

Is there anyway to lower the transaction fee in multibit?

I am getting this error, and I already have all the blocks downloaded in the %appdata% section.

Right now I have a i3-2100 with a 550ti and I am planning to upgrade the 550ti to a radeon 5970. I am quite sure the 5970 might bottle-neck when gaming, but will this also affect BTC mining?