I wouldn't recomend the SSE as a second plane. It is a great third or fourth plane, but a bit too responsive for a second plane.
I'd recommend the 4*40. You can take a bit of the dihedrahl out of the wing and make it more responsive. It will still be very easy to fly and land.
I have a friend who got the SSE after he soloed on an LT-40. I told him not to do it, but he wouldn't listen. He made it past the first 3 or 4 flights, but he smacked it up really bad on the 5th flight. Total loss. It got ahead of him and he over-corrected too many times.
Even with a flat prop- it's just too much plane for a second plane. Most guys will use the 12.25"X3.75" APC with a 46 engine on this plane. Even that will not tone it down enough.

I soloed with my LT-40 and then I continued to fly it regularly for about a year. In that time, I learned inverted flight, rudder turns, flat turns, hammerheads, touch and goes, and even rolling circles(best way to learn how to do a rolling circle). I flew that trianer untill I was so bored with it that I just couldn't stand to fly it anymore.
THEN, I got out my Kadet Senoir that had aileorns and a 120 4-stroke. It was a taildragger. I learned the basics of the taildragger quickly and moved up to a Hobbico Britestar after about 3 months on the Kadet Senior. The Hobbico Britestar was my first low wing plane-- still a flatbottom airfoil, but a low winger.
After the Britestar, I got a Joss Stick. It was an ARC. I turned it upside down and made it a low wing taildragger. 120 4-stroke for power.
After the Joss stick, I built my first aerobat. A Lanier Laser 200 25% with an MDS 148. And I've been flying aerobats ever since.
The total timeframe for all this was about 3.5-4yrs. From the time I soloed on my LT-40 to the time I first flew my Laser 200 was about 4 yrs.
I'm a pretty decent pilot. No TOC champion, but a decent pilot now after 6 yrs in the hobby.
My point to all this is simply; TAKE YOUR TIME. Enjoy the building process. Enjoy flying different types of planes BEFORE you jump into a full tilt boogey aerobatic plane like the Sig Somethin' Extra. There's no rush. Rushing into an aerobatic plane like the SSE might just end up costing you a bunch of money.