You don't *have* to rear-tether if you don't want to. It prevents rebound, which may or may not be a concern to you. Depending on your vehicle (it's not one I'm familiar with), it may also not be possible, for example if you put it in the middle of the front row of seats but have captains chairs in the front, there might not be a way to tether it without twisting the seat. It can also be useful - if you need it - in helping to acheive a more reclined install as you can tighten the rear tether to pull the seat back down.
As far as Premier vs XT goes: both are considered to have side-impact protection though obviously the head-wings on the XT will do more. However they're really only effective for FF and can't even be used (need to be pushed all the way up) when the bottom 2 harness slots are in use, so if you have a short-torsoed child it may take a long time before you can use them. A few people have mentioned that it makes it more difficult to lift a child in and out of the seat with the headwings as well, so if you have any shoulder or back problems this may be a concern to you. You may also have a cover preference; we were talking to a tech when deciding on ours and she told us that the mesh covers (each model has one) wear really quickly and for some strange reason take a really long time to dry if you ever need to wash them (with an 8 yr life span, this will happen eventually). When we got in a crash recently, the cover that we'd bought originally wasn't available locally so we picked up one with the mesh cover and she was right about the wear: one pair of velcro-closure shoes and a 10 minute car ride and you could already see that the mesh was fraying. Poor choice of fabric, IMO. But the non-mesh covers are great, the fabric is so soft I'm actually jealous that she gets to put her face on it and I can't.
When it comes right down to it, though, either version is great and it's mostly personal preference.
Good luck - but whatever you choose you're choosing a great seat!
Melissa
