Go for it, as the experience is worth it as a rite of passage.
I remember going from a 2000 R6 to a 2004 R1 after 2 years of street riding, touring around the UK, and plenty of track days on the R6 (and unfortunately track crashes).
That 3rd gen R1 was like a beefed up 600...Not much torque down low but a linear kick in the arse from mid range to about 12k revs and, I don't know if it's to do with Yamaha's musical heritage, but the sound of the motor coming on song was incredible to my ears (that may have been a lot to do with the buying decision when I test rode it).
You can't beat memories like that, and I found I had to finesse some elements of my riding, taking classes with California Superbike School up to Level 2, and reading theory, all to make the best of a bike which handled better than the 6 but had about 60 HP more. I believe I became a better rider after jumping on a litre and deciding to try to understand better how a bike works.
However....After many years, and many miles of more touring (around Europe), many more track days, and even an attempt at racing...My daily rider is a 2003 SV650 and I love it (especially with the GSXR 1000 front end and brakes). I took it to Aragon in Spain for a track day and although I got spanked on the straights by V4 Panigales and S1000RRs, I caught them up in the corners....You can't beat memories like that either.
TLDR...Buy the K5 GSXR 1000...btw 42000 KMs is nothing....Suzuki build some of the best motorcycle engines in the business...especially gearboxes...They just cheap out everywhere else
Ride it for a few years, then keep it as your special bike where your daily rider is a lower capacity lightweight bike...Even a Ninja 400 would be super fun.