I'm not going to talk much about the sound, a thousand reviews and countless listeners and professional musicians already know. I tried 11-49's at full tension for a while, they have a lot of nerve but they prove hard to bend. So now I'm only putting 10-46's and 9-42's on my axes.
I found an excellent Madison Strat clone with 22 frets and a very well contoured neck joint so it naturally begged for shred strings, and that means 9-42's. Their unplugged tone is exactly the same as heavier D'Addario strings except the biggers ones have a kinda boosted sound all over the spectrum.
I was afraid that would be heard drastically at the amp but no, they level out when amplified, maybe because the pickups need to be a little closer to the less massive strings. However the main reason for the 9-42's was comfort and I got plenty of it. They feel like hair, they bend super easily but not so much that you don't feel a tactile feedback, they do resist a little bit.
For some reason they detune more after bends than after trem motions but they don't detune more than heavier gauges. By the way, the 11-49's I still have will be mounted on a guitar that has an unusual strong resonance in the low end, I will tune it in D standard and enjoy the fat tone. Full tension with 11-49's was an experiment worth doing but the playability of thinner strings is hard to live without.
Comfort should be the same than 9-42's, I guess. I also bought a super affordable Stagg Strat clone with only 21 frets but the neck feels so fast to me, I'll be putting these 9-42's, too, it will be my other shred guitar, and it might prove faster because of the ergonomics.
To be sure to exploit that speed it'll be fitted with these soft 9-42's, the stock 9-42's don't sound great but they feel right so D'Addario tone has to complement that comfort.
Edit: when I switched from fat strings and soft rounded picks to thicker pointy picks and thinner strings the attack remained sharp.