and I have heard ti is a bad material for heavy riders. it has more flex than steel and so when you put a big fellow on it like yourself it might feel kind of squishy : )
Ignore anything that person says in the future. Ti is a perfect material for riders of all weights. Of the two makes you mention, Merlin is still > Litespeed although the geometry of the Lites is a bit better for climbing.
Re: 3 vs 6. As a heavy guy (210 lean, 6'3) and owner of a few Ti bikes including two Merlins (1 roadie, 1 mountain) and A LS Tusc I would argue that you want to look at geometry first, second and third.
Regardless, I'd have seven build me a frame. Merlin went downhill after their acquisition and loss of everyone good and Litespeed was never really all that good in the first place.