In most cases, performance cams are to increase rpm range to get more hp that way. They often do not help at the rpms that you said you ride at. But they will give a noticeable power bump at rpms higher than 4000rpm, at a possible reduction of power below 4000.
The best things you can do to increase torque over the entire rpm range are increasing compression or displacement.
The 612 kit is a very big labor job, in addition to expense.
My advice is to increase compression by doing the "squish mod". It is very low cost, and moderate labor involved. If you are capable to pull the barrel, you can do it. You will need to measure(with a depth gauge) the depth of the piston down the bore at TDC from the deck of the barrel, with the head and head gasket removed. And you need access to a machinist to machine the deck of the barrel down that same measured amount(about a mm or so), so that the piston will be flush to the top of the barrel at TDC. The amount to machine off the top of the barrel will be the same as your measurement that your piston is down the bore from the top at TDC. Maybe, you may need to shorten the locating pins for the head if they stick up too far after the mod, which is simply grinding them a bit shorter.
Then, upon reassembly, the thickness of the head gasket will set the proper squish distance.
That's it.
It increases the compression and creates a squish function for improved combustion efficiency, so it should not ping. If it does ping, you might need to use mid-grade 89 instead of 87. We have not seen that need, but in interests of full disclosure, increasing compression 'might' need a couple more octane points. My experiences indicate that you should still be fine with 87 after doing the squish mod.
It gives a small(but noticeable) torque and hp increase at all rpms, improves responsiveness to throttle input, and should show a small improvement in fuel economy mpg.
Cost is very low. A small machining fee, and some new gaskets.