How are you currently managing these 750k photographs. Although you and I seem to be alone, at least in this thread, in finding LR clunky (compared to PS, and in my case Capture One and PS), it should still be useful (over Bridge) for managing this number of photographs.
Even if you just use it as a DAM and immediately transfer images to ACR/PS for processing. On Import I have templates set up that automatically add metadata. This makes searching for something like all photographs taken from a particular location over a particular date period really easy, and much, much faster than Bridge, even though Bridge indexes the same metadata. I also make use of keywords a lot, which also adds to the value of a DAM, but that's of no value if you don't take the time to keyword images.
But how valuable this is obviously depends on how you need to manage your photographs.
Having said that about LR: scrolling through my library of pictures (50,000) is one example of where LR is tediously slow compared to Capture One, but both are still a lot faster than Bridge. Other than scrolling speed, LR is a far better DAM than Capture One in almost every respect.