What effect will these have on the handling balance of the car?

I ask because I'm trying to reduce the oversteer tendancy of it at the moment. I'm going to reduce the camber at the front (to even out the front / rear grip) but I'm wondering if it's worth upgrading to these bushes too.

Will they increase oversteer, or will they reduce it?

It shouldn't make any difference apart from replacing the tired (and no doubt) bushes in the subframe which can make the rear of the car feel like it's catching up with itself when cornering hard and making small adjustments to the steering input

I think I'll hold fire then and see what happens from tweaking the other bits first. It is a bit vague at the rear end at the moment but it can wait.

Thanks for that.

Why reduce front end grip? Why not work to improve rear end grip instead?

If the rear end is feeling vague then it certainly sounds like its time for a refresh back there, new bushes and new bearings would make the world of difference.
Just out of interest, what anti-roll bar is on the rear and what dampers/springs do you have?

I'm running the following set-up:

Bilstein dampers
Eibach springs
22mm Whiteline rear ARB
Camber bolts Left -1°20' Right -1°18'
Sparco strut brace

I'd be very happy to improve rear end grip but didn't think I had many options. As above, I was thinking that new, uprated subframe bushes would help. I'm going to dial out camber to -1°10' anyway as it feels like too much at the moment.

I had new rear subframe bushes fitted last year and noticed no difference with the handling or balance of the car, although my reason for changing them was due to my old ones being severely worn and starting to eat my rear tyres, not for handling reasons, I'm happy with the way my car handles