Your looking at a wide range of bikes which are mainly XC, the Giant being more AM, along with the Stumpjumper depending on year. The Trek & Rocky Mountain are at opposite ends of the market, with the Trek being a high end carbon frame & the RM being bugdet aluminium or high end carbon depending on the year.

No matter what you look at, expect a lot of your current parts not to fit a newer frame, and not sure what benefit you are expecting to get putting a set of 28mm SID's on any modern bike, as it the front end will be very flexy. You may find that the SID has too little travel for a 3 year old frame, if the SID is 10 years old, it is probably 80mm max travel, most frames which are 3 years old will be designed for 100 or 120mm travel forks.

For size, you mey get away with a 17" but probably not 18", but you really need to try each individual bike built up to know this. Whats wrong with the size you are currently using?

For the frames your looking at, 3 years in full suspension design with either have stayed the same, or radically altered manufacture dependant, also a 3 year old frame could need a lot of work, so budget for a shock service & bearing / bushing replacement whatever you choose.