will a i5 2400 chip run sonar platinum with ease or should I look for something more powerfull.Its a pc tower with an 1155 socket. perhaps a chip upgrade?

Personally, given the choice, I'd go for an i7 rather than an i5.

However, if the choice is between an i7 and a very much faster i5 then the i5 may win out. Much depends on how you use Sonar - e.g. plugin and software synth usage - whether it would benefit from the i7's hyper-threading.