Keep the one that "fits" you the best. This means more than just a fame fitting, and frame size. Different frame sizes feel different to you, even in the same bike. That also includes how it feels when you ride it, and what it looks like!

It's always "normal" to have buyers remorse - and you will get over it, as you make your bike your own.

Assuming you are going back to test ride them again, make sure you do the little things, like make sure the seat and bars are the same height and angle, the tires have the exact same pressure in them, you have the same shoes and clothes - these little things help you compare apples to apples.

Looking at them side by side, the Sirrus is the more "heavy duty" of the two, due to wheels alone - at that weight level, we're not talking "weight weinies" on either one -

Personally, I like the looks of the Sirrus better, and it comes with more "included" stuff - like bar ends, Mavic rims, 32 spokes, and Body Geometry seats are really pretty comfy seats -------

Back in '08, when I was test riding FX, and Sirrus, the Sirrus felt the more "solid" to me - and I don't recall feeling any weight difference. i just needed the suspension for a back problem, and I liked the Crosstrail better than the 7000 series treks "It just felt better". I guess that makes me a Specialized person. (P.S. I tried lots of other manufacturers, too)

One more thing - I would have the LBS or a known GOOD wheelbuilder, "re-tension" the spokes - with a METER, even brand new - it will save you a lot of grief later on. It will be worth any added expense.