Bests & Worsts Reviews from Amazon

Title line says explicitly 4TB 7200 RPM. I noted a drive going down on my Drobo and ordered on Sunday; Amazon had it at my door before I left for work Monday am, so that was amazing... but that also led me to quickly insert it to start rebuild before I left for work. It estimated 10 hours so it would be done by the time I got home. Now home it claims 4 hours left and Drobo says it is really 5800 RPM. Checking my order again, indeed the title claims 7200 for the 4TB, but lower in the ad section where it says in large text 7200 in smaller text underneath is says 5900 for 'lower capacity' versions. Finally in the product comparison it claims it to be 5900. It however is not even 5900, but rather 5800. Now I've got this inserted and nearly merged into the RAID data set, so it remains to be seen whether Amazon will agree to take it back. Were I to leave it there it would compromise the performance of the box for as long as it remained in place, so that is not much of an option. Perhaps I will let it finish and then do a disk benchmark to quantify the slowdown before deciding, but very unhappy with the situation.