Friend of mine just put Gut in his Blade 98's which are reasonably stiff. Took him some adjustment coming from a poly. Was hitting with him yesterday and he was 3-4 inches long at first on deep trading rallies but by the end had it dialled in.
I only use gut in all my frames. I like my shoulder and wrist. they last twice as long as other strings in an 18 x 20 so even though the cost is higher up front the playability and tension maintenance is superior to any other string.
Had been using gut for 30+ years. Haven't played now in 8 years due to health issues and bad knee. Just got knee replaced. When I start playing again (hopefully within 3 months), I'm going to try a thin poly strung at 30#. Just before I quit playing, I tried Solinco Revolution 18 at 30# and it hit well. The main issue is that it didn't make any sound. Now, after not playing for so long, I'm hoping it will be easier to adjust to not having the sound that confirms a nice hit.
I use gut mains in my Yonex VCORE Pro (330g) which I consider to be fairly stiff. My favorite setup is Klip Legend mains and Max Power crosses. I tend to get arm issues hitting with full poly and my swing speed really isn't fast enough to take full advantage of it anyway. I think a lot of people would be better off with this kind of hybrid, but full poly is all the rage these days. Sometimes I'd like to go back to full gut, but most racquets are so powerful now it's hard to control and I hate dealing with string movement.