Well they don't feel one in the same in the hand to me.
The gas system may be the same, but they way they feel in hand and should are different enough to me to warrant handling both. I also see the SX4 as a great gun and was about to buy one when I found the Maxus for slightly less. I couldn't stomach the price of a Maxus after having 2 Benelli's and not feeling they were worth what they cost, so I had decided to try a 26" SX4 for an all around gun. I found the Maxus on Buds at what I think was a mislabeled price for $875 and immediately hit buy now. The next day same gun was $1400 again.
I think I could be perfectly happy with the SX4, but the Maxus has always felt better to me.