Revel GEM or Wilson Cub 2 ?

"I was quite surprised, how good the Cub 1 performed in that area and need a speaker that can deliver at least 50 hz at higher volumes."

Why 50 hz at high volumes? What are you purposes/uses/expectations, for the speakers? Are you planning home theater? Or just 2 channel stereo? And, if a big room, why smaller monitors? I'm confused here. If Home theater, you're DEFINITELY going to cross em over much higher anyway! Or at least you SHOULD.

I´m sorry for confusing you. My room has only 20m². 2 channel stereo only!

I don´t need a speaker being capable of playing at high volumes but it should offer full range sound at low/medium to slightly higher volumes.

Er, um, Ok, so why smaller speakers? I'm confused.
Whatever, anyway, I think the Cubs play lower, yes, and they're probably more sensitive and dynamic as well, all things equal. However, the Gems are more flexible a bit. Wilson recommends keeping Cubs on "those stands". I like more flexibility, depending. Still, you're in the same league with these. I'd still go large speakers though.

The LE1 is not a reliable sub amp according to someone that used to work at Revel. I would go with the B15 subs. I had also considered the LE1 but decided to go with the B15 which has worked well.

I have used Gems for a long time as my main speakers and really-really loved them. I had two Velodyne DD18's crossed at 80Hz to support them as their bass-response isn't all that. Recently I have upgraded to the Salons and moved the Gems to the back. Although the DD18's were very impressive I upgraded to a pair of SUB 30's.

Wilson may be faster and may sound a bit different from Revel. But Revel is my sound. I promise Gems will not let you down, but listening to Revel's first won't hurt.

The Sub-15 and the LE-1 were very good when introduced (10 years ago), but I believe the amp (LE-1) had heating-problems and the subwoofer could clipp when pushed. Revel build the SUB 30 taking care of all know problems the SUB15 + LE-1 had.

I would get the Gems and start looking for a SUB30 or a Velodyne DD18. The SUB30 used a dual 15" woofer AND has room EQ. Personally I believe you can have two or more subs in your room. It's not all about output. Having multiple sub will result in a more evenly spread bass-response anywhere in your room.