Kenny probably knows more about B23F's with K cams since he's a moderator now, but I'll weigh in on this anyway.
My daily driver 245DL with B23F engine had a K cam in it for 2 1/2 years. I took it out about 2 months ago when I wanted to test it against the B cam, and have yet to put it back in due to the results of the test.
About the K's performance in my car: I have a stickshift, so it is much better suited to my car than it would be to an automatic. Idle is not affected at all. Gas mileage goes down maybe .5 mpg. Powerband when timed straight up is 3,000-6,000rpm. Below that, it's pretty weak, but still driveable if you don't mind leisurely acceleration. If you advance the camshaft 6 degrees like I did, driveability drastically improves. Powerband starts just above 2,000 rpm, and continues until 6,000 rpm. It's a nice cam, and is well suited to the application if you must have high rev power, and have no other choice in camshafts.
I did have a choice, so 2 months ago I tested out a B camshaft to see how differently it performed compared to a K. The B is much more streetable. It performed 10% better in low and low/mid power, and was only about a tenth of a percent behind in high rev power. When timed straight up it has a 2,000-6,000 rpm power band. It pulls much better between 1,000-2,000 revs, which contributes to it's streetability.
I would suggest the B over the K cam, but if you plan on heavily modifying the engine, i.e. head work, better intake, headers, 2.25" exhaust, etc, then the K may end up being better. My car, when I tested the cam, had these mods already: Electric fan conversion, 2.25" exhaust, slightly modified intake, and advanced ignition timing, plus more powerful ignition coil.
I'm sticking with the B cam, and am very happy with it. In my opinion, the K cam overcams a stock or mildly modified B21F, B23F, or B230F.