Iphone 2g was good on ios 1, slow on ios 2 and very slow on ios 3, so after 2 major updates it got slow, so is the iphone 3g on ios 4.2 and iphone 3gs. Iphone 4 is running ios 6, it is the second major update and it should be slow like the others above, also it is a bit slow on ios 5 and a bit laggy on ios 6. Now if I buy an iphone 5 with ios 6 and update to ios 7, will it run as slow and laggy as iphone 4 on ios 5? and if i update to ios 8, will it be as laggy and slow as iphone 4 on ios 6? Or it is going to be a fast phone even after 2 or 3 major updates ? I know, the post is long and a bit hard to understand, sorry.