The difference in length isn't really noticeable.
The only thing a performance mid section back will do is sound louder. Which spoils one of the car's better attributes.
Not to mention the fact that it’s rusting, which I find odd for a stainless steel system
There are different grades of stainless in exhaust systems - 304 and 409.
304 is pure stainless and will not rust
409 has some steel content for flexibilty, but will rust albeit slower than a mild steel system.
Most silencers, especially back boxes on stainless systems are 304 and polished for appearances.
I have had a complete 304 stainless sytem on a 1967 Triumph 2000 for about 25 years with no rust showing on it at all. The hanger brackets and clamps are also 304 as these are the parts that severely rust if mild steel.
I also have a 304 stainless system on one of my Omegas from the cats back. A nice sound, maybe slightly drony at speed, probably more noticeable being an estate. It was on the car when I bought it over 10 years ago, and has no rust on it whatsoever.