Need to keep the cost below £1k when using education discount. Options are either the i5/256 or the base model upgraded to an i7. Main use is predominantly iOS development as have PC for gaming. Was getting by with a 2012. Have NAS and external SSD storage, but wonder whether the impaired write speeds of the 128gb internal SSD bottleneck the i7 and mean the i5 would compile quicker. If not, would go for the i7. Would appreciate thoughts. Thanks.