Getting back to the original question...
It's very unlikely to be worth it to increase the rear bar by 0.5mm. The difference is academic. Tire compound/size/temperature/pressure, road surface, and nut behind the wheel will dominate any small change like that. Lotus Sport makes bigger front and rear bars. I believe the part numbers are: ALS5C0089J (Front), ALS5C0090J (Rear). Some of us contend that even these are too small.
The evora suspension is an interesting compromise between comfort, performance, and *budget*. If you're willing to give up one, you can certainly improve the other. Personally, I'm willing to give up a lot for better transitional response. Therefore I'm a fan of big, big bars. Well that and the fact that the SCCA doesn't let me change springs. :-p