I don't have any horizontals and other than a GR510 my biggest machines are VF2 without gearboxes so I cannot comment on rigidity issues or machining tough stuff.
And if anyone asked me to machine Inconel I think I would running screaming off the nearest cliff.
Regarding reliability I have found Haas good, actually very good except for a blip around 2004 - 2006 when their attention to detail on final assembly seemed to slip. Several machines needed finicky little fixes during warranty.
My last two or three machines have been fine so they must have tightened up a bit.
Do you know there is a 7% price increase July 1st at Haas; you may need to do some quick decision making if you want to save a bit of money.