I have the 3 in 1 and the TM260 on one boat and I have the TM265lh on another boat (same low frequency element as the TM275lhw).
The TM265lh is definitely better than the TM260, and the TM260 is definitely better than the 3 in 1. I think the 3 in 1 is only 300w output or something for normal sounding so is not that grunty. I only ever really use it for side scan.
For 500m you would benefit from the TM265lh or TM275lhw over the TM260 for sure. But they are about twice the cost, so really depends on how much time you spend out deep. For snapper and kingis the TM260 goes mint, I easily mark sign on the bottom in 50m when doing 20 knots. Its really transducer placement that helps with this.
With the TM265lh I usually have low chirp running on one screen and high chirp on the other giving me the best of both worlds. The high chirp on the TM265lh has a very narrow beam which does make it good for penetrating deeper and giving better detail, the only downside is there is less coverage off the bottom and fish sign in say 50m, but when I have the low chirp running I get that anyway as that is a wide beam, so the best of both worlds really.
Hopefully that is somewhat helpful.