THe 1995 E300 should not be much slower than the 2.5T, spec is about 1 second slower to 60mph (about 12.5 instead of 11.5 for the 2.5 turbo, or 10.5 for the 3.0 turbo.) The W123.133 (older 300D turbo) is around 14.0 seconds.
That said, it depends what you want. Feel the need for speed? Get a 1987 mint condition, preferably with new head, or budget in $3k for a future head job. The power is addicting. But you may need to spend MONTHS finding the right car, and it's guaranteed to be on the "wrong" coast relative to where you live. You can swap on most of the late-model goodies to make the 1987 more plush, like leather/wood door panels, etc... I've done that to mine and I love it. (see photos by clicking the 'www' button below.)
If you want peak fuel economy, and maybe some more cosmetic bling and/or interior comforts/features, the 2.5T or E300 are good alternatives (but at higher cost). The benefit here is that it should be easier to find one in good shape, possibly local. The 87's are rare, the 90-95 are not (well, relatively not rare, compared to the 87 anyway.)
There was never a turbo 606 engine installed in a W124, ever, anywhere. The one on eBay is a stock non-turbo. That model got the vented right fender for looks I guess.
Side note: Mercedes brakes are directly related to the engine power output. The E-class with the M104 engines (93-up) got larger brakes, as did the M119 (1992-up V8). The diesels did NOT, they use the same as the original 87 300D. The only viable upgrade is, IMO, the early 500E brakes which I am in the process of doing on my car.
