I have an LMS-350A and an X-18 that I use on my boat.
The LMS is almost identical to an X-70A with added bells
and whistles and GPS. I have used the fastrac on both
units of an on but never used it that extensively. It shows
a flasher type vertical real time bar.
For ice fishing I use the Vexilar FL-18. It really does excel
in ready what is happening below you. Like other state, you
can see a 1/64 oz jig in 50 feet of water with ease. The main
difference I see between the LCD fastrac and the vexilar is
the ability it tell were fish are in the transducers cone. The
unit uses 3 colors to help you determine if a fish is to or away
from your offering. You can adjust your presentation to entice
strikes just by watching the reactions or mode of the fish. On
an LCD you can see a fish move up or down to your bait but
may not be able to see its horizontal movements which may
be the most important sometimes.
Also I don't think you are comparing apples and apples. The X-70A
back in the early 90's was one of Lowrances top end Walleye units.
Although the Vexilar is $500, if you were to buy a unit now similar
to the X-70A it would be the LMS-320 which is over $1000 and almost
$2000 after taxes with GPS.
Good Luck choosing,
I always buy what my wife wants,
Whatever keeps me happy she saids,
She let me get the Vexilar,
BATMAN