I Have both the Sage X and Igniter in 7wt.
The Igniter is an out and out distance rod, very powerful.
I very rarely use the iginter, its good on windy days, striking fish when fishing deep on sinking lines and setting the hook when using the bung at distance.
There is very little flex and its not forgiving. It can easily handle an 8wt line.
The timing of the cast has to be spot on for the igniter.
From reading the blurb from sage the iginter was designed with power and high line speed to cast into strong winds like off the beach and places like patagonia.
The x has more flex and I can fish dries without fear of snapping off on the strike.
I can't comment on the 6wt iginter but in my experience of sage rods ,there is generally a big difference between their 6wt and 7wt rods.
The 6wt iginter might make a nice 7wt rod.
My opinion is the x is a better all round rod in a 7wt.