I think the key with having a quick running site is more a usability one, if the site runs slow especially e-commerce users will bounce to other websites and competitors.
Site speed has been noted as a small factor to ranking yet their are 100s of ranking factors.
Godaddy servers are not the best at all from my experience, I have tested a few servers their a while ago, depends on what type of server you are after too - dedicated server, shared host ect.
Also up time of the server is another important factor, geo location of the sever i.e is it close to your main user base is also important with e-commerce.