I think any Kawarthas fish over 44 is a very good fish!! Any fish over 40 is a nice fish and worthy of some high fives and pics.
I fish the Kawarthas regularly and get lots of fish and you have to put a lot into the boat before you get a high 40's fish (although yes it could be your first). Over 48 is definitely VERY rare.
I have only seen 2 fish firsthand over 50 in the K's and they were not landed - so they may have been smaller.
A good angler I know, who fishes skis 20 days a year minimum, has landed one fish over 50" in 20 yrs (that is 1 in 400 trips), so when I hear Kawartha's musky guys say they got 4 over 50 last summer I just laugh. It is possible but mostly likely Bull.
I think the "magic 50" number has become a ridiculous benchmark. It is a recent internet phenomena and just another ego-building bragging point. I would take a fat 48 over a skinny 52. AND, it makes me angry to hear Bob Mehsikomer measure a 49 and then proclaim "rats... well that's a decent fish anyways!!???" That just puts unrealistic goals in his viewers' heads and it belittles other's accomplishments. A trophy could be anywhere from, 30 - 50 inches depending on the person. If a trophy is a truly rare, almost never caught size - then a 50 in the Kawarthas is the number I guess - but who cares really - just go fishing and enjoy what comes your way.
I just hope for a bigger fish than my PB, but I shoot for that for myself, not to impress others.
I personally enjoy casting them up and the Kawarthas are great casting lakes.
My PB is a very fat 46" fish that weighed 25 pounds (casting St. Clair) and I was very pleased. The next cast, seriously, I had a follow on my bait that made my 46 look small. True story. It was longer and grotesquely fat.
The Kawarthas are likely the best place in North America for casting good numbers of decent sized fish (38 - 44). Americans come up here all the time from Wisconsin to run the numbers up on decent sized skis.
Landry