340 performance?

You disagree ? But agree ?? Let's start with were you disagree - and I agree only from personal experience. My 8 1/4 never broke before I sold it and that was with 355's and 26 inch mt cheater slicks and many passes with a 4 speed, the old 318 and new stroker motor ! So I wanted to try 410 gears and 28 inch Hoosier's. Now I felt I was starting to push my luck and the 8 1/4 had served well, it seemed only a matter of time and again I got lucky and sold it before it became worthless or got me hurt. Spent a grand and built a 489 case 8 3/4 , spool, new 410 gears, professional set up- on about my 30th launch ka booom I damn near sent the ring gear through the back of the housing. Now would I have been better off juat leaving the 8 1/4 ?? And of course to the op this has been my experience and remember I don't know crap.
to were we agree - slicks! To this day I haven't spent better money to make my et lower. As far as gears ? I think it depends on really how much you want to bring it to the track? A couple times a month and maybe start bracket racing - sure. Once or twice a year - don't waist your money.