This is an interesting question. My Ericson 32-200 has more rake than the tuning directions seem to suggest. I have let the backstay out as much as possible.
Mast rake is set with the forestay, not the backstay.
Just for grins, as I was setting the mast rake on Abracadabra this spring, I experimented with backstay tension. Made no discernible difference.
I also seem to have a lot of weather helm in some conditions.
Too much mast rake will do that.
Our boat is billed as a cruiser/racer. I believe your boat is, too. I set our mast rake to about 1-1/2 degrees. (I think I used Giu's numbers for doing the calculation.) We can literally let go of the tiller on most tacks, under most reasonable conditions, and it'll stay put. Going to weather, under reasonable conditions (i.e.: Not on her ear), she's got just a touch
of weather helm, which is just how we like it. By "touch," I mean we can still let go of the tiller, but she'll eventually begin to gradually head up.
See also Giu's new video on using the mainsheet traveller. Even if your boat is in trim: If she's on her ear you'll be hanging on to the tiller or wheel for dear life. De-power things a bit, let her stand up, and she'll be going just as fast, probably faster, a lot more comfortably and with a lot less strain on boat and crew