Judging by your setup... did you pick those two just because they are high-end boots..? Just because they are top-line boots does not really mean they are going to be the best for you or even fit you right.
there is definitely something to be said about a good liner in a boot and a good design that will maintain stiffness as well as a good lace setup...
But for the love of all that is holy.. try on a shitload of boots and buy whatever boot fits your width/length and locks your heel down tight.
If you really care about your riding and want to progress and be comfortable then listen up:
A GREAT FITTING $250 BOOT IS GOING TO SERVE YOU BETTER THAN A $500 BOOT THAT DOESN'T FIT RIGHT.
If you already spent that kind of money on a board and binding... yet need to ask people on an online forum what they think about a boot. I am going to make some assumptions about your prerogative. Having super expensive gear does not make you a better rider nor mean it will best suit your needs.
My apologies for the rant/troll or whatever you want to call this.. I just see way too many people asking on a forum what boot they should buy and IMO it doesn't matter what the internet people think.. buy what fits YOU.
There is a reason I do not buy boots online.. I have even tried on a couple pair of the exact same boot in the exact same size and found one pair fit me better than the other (and it was the exact same boot & size).
I chosed the SLX becouse it's a responsive boot but not responsive as the ION and it's comfortable to that's the reason