Hi Terry, torsional flex in a chassis is a good thing, as it lets the chassis load progressively in a corner, and you will find all "high end" scratchbuilt chassis incorporating it. It is equally important to engineer in the correct amount of flex, and as a general rule of thumb,.....the quicker the motor, the stickier the tires, the faster the track, the stiffer the chassis...With the opposite being true of course.
The FF050 motored F1 cars with their skinny tires, low powered motors, and, racing on club tracks can be quite "soft" indeed, and to be honest your 1.2mm torsion bars are massively thick/stiff. I find that most of the scratchbuilt "Flexi board" chassis that I have seen in either proxies, club racing, or, brought into the shop, have been far too stiff.
In similarly motored chassis, I have never used anything thicker than.032 (.8mm) and this was with very long bars.....most typically I use bars between .025 and .030, depending on their length.
Cheers
Chris Walker
A couple of shots of some F1 chassis using "thin" torsion bars...............these have all won the proxies they ran in.