I have a 550FS in 6.5x55. I only have less than 40 rounds through it though. Started out OK, but then accuracy started to drop off. I pulled the scope (an old Weaver K2.5) and shot some nice groups with the open sights. I think it was a scope issue, but I need to play around with it some more to confirm this.
I was asking myself the same question you asked in the past, and most of the posts I found indicated no issues. Someone will chime in who has tested from a variety of positions with the barrel hot or cold.
If you get a 550FS, know beforehand that the sight radius is, uh, really short. NECG makes a peep sight for it, but I don't think it fits the classic lines of the rifle very well. The rings that came with mine (bought it used) hold the scope up pretty high -- high enough that the cheekpiece rests against the side of my jawbone.