The JVCs are some of the quietest projectors out there. If noise is of concern you'd be hard pressed to find something quieter, especially at this level of performance. I've owned three JVC models and they've all been super quiet. As far as the bulb question goes, it depends on how large your screen is.
Edit: I think the RS4810 is the equivalent to the RS55, not the X55. So I'm not sure if my comparison is relevant or not.
No, you were right first time the RS48/RS4810 and X55 are the same projector. I own the X35 (RS46) and can also confirm that high lamp is noisy, much more so than the previous HD350 (RS10) I owned. I use mine in low lamp, but if it dims enough to need high lamp I will have to buy a new lamp or watch loud films.
Zooming: Been there, done that, bought the lens...