Well, see I do play runescape, and I run multi bots (java scripts) which are coded to do actions. I dont know if I should get a 2600k or a 2500k now because of the hyprothreading, I am not sure if it uses this or not. I assume it would because the bots are very cpu intense and it has to feed code in a fast rate to keep the actions going.
Possibly, but most enthusiasts feel the extra $100 is not worth it as it doesn't make games run any faster. The i5 is a good choice, most software (still) does not take advantage of more than 4 cores.