Frank -
I can't speak for all Merckx bikes, but there are several in the stable, all ride superbly. Merckx is very demanding about build and geometry. I believe it was Chuck S. who remarked "There may be frames as good as Merckx, but none better." You do need to keep in mind who the "audience" is for a Merckx frame, all of mine are racing frames, not racing type, but true ex-professional frames, now out to pasture. Consequently, if you aren't up for the ride and handling, it can be more than you signed up for. My wife has ridden a MXL frame, lugged steel, and although the fit is pretty good, she's just not big enough to be comfortable for more than 2 hours, whereas she'll cruise for 2 to 3 times that on her Bianchi. That said, for her, the MXL is the much quicker bike of the two.
I do have a 7-11 Century in SLX, haven't built it up myself yet although it's near the top of the project list. I suspect it will be damn comfortable once I do get it on the road.
Sid, just in from my evening ride, and smokin' in the Midwest heat wave, Smith