The bikes with the OFF-LO-HI switch will slowly warp the plastic contact supports when using the 60/55W H4 (that's what I have in my 750K2). It takes about 5 years of my riding time to do it. I make the Dual Relay Kit for those bikes.
The bikes with the ON-OFF on the right and the LO/HI on the left only need the cheaper single-relay kit.
The bikes with only the Lo-Hi switch on the left need the Start Button Saver relay kit to save the Start button from self-destructing with the higher-wattage bulb.
In tests I did years ago (1990s era), the 40/45w H4 bulbs were slightly brighter and further down the road than the stock Stanley bulbs in the 750. The next step up in H4 is the 60/55w bulb, which then started attacking my headlight switch(es). When I could not buy a new one (in 2002) I created the dual-relay kit, sort of from need: I like the 60/55w bulb at night for my older-than-my-750 eyes.