S-148's all the way around, on mine, in keeping with the whole "cheap ARF" thing.
The 537's I have feel about the same strength. Dunno the specs.
(Yes... weak enough to stall by hand, holding ELE or RUD and moving stick. They're fine in the air)

I will say now, after a few flights' experience, it's pretty hard on the battery.
Earlier I told someone that the pull-pull system wasn't that bad.
After noticing that I can't do a flat spin, after four flights today, I may modify my opinion

I based my previous opinion on flights consisting mostly of rolls, loops and touch-n-go's.
The past couple days, I've really put the plane through the wringer... mostly snaps, spins,
blunders, tumbles, and some maneuvers that are yet unnamed, and too scary to think about.
(The result of trying manuevers that I'm not competent to do yet, I'd guess. My poor, poor wing )

Best I can tell... after the battery has drained somewhat, there just isn't enough OOMPH,
and either the ailerons won't force it flat anymore, or the elevator starts giving up at that point.

There's still no problem "flying", but the fancy stuff is pretty much "out".
I'm sure the drag of the pull-pull rods are accelerating battery drain a bit.
The pull-pull setup is quite draggy. More than I had thought, previously.

Whether stronger servos, or a stronger battery, or fewer flights would help my case, I don't know.
I don't plan on changing anything. I just know to bring it on home when it won't flatspin any more.

I suppose if I had wanted to spend any extra money on it...
stronger/faster servos, and cables for the pull-pull would've been where I spent it.

My only mods were:

"Battery above elevator servo", so I needed no tailweight with my .46SF.
Z-bends at the ELE/RUD servos, instead of using a 90 and the *loose* snap-keepers.
Cable for throttle, since I mounted the .46 at 120 degrees, to have exhaust underneath.
Aileron pushrods I had in my spares box, again, using Z-bends instead of 90 & snap-keepers.

I just didn't like the way any of the snap-keepers fit, and I hate for stuff to "disconnect" in flight.