That's great that you consistently work on finger legato. I am a strong believer that we should not be overly dependent on the damper pedal. So when I'm practicing I'm always conscious of trying to hold notes to full value to the practical extent possible, as well as ties. Where that's particular difficult or even impossible, the pedal then earns its keep. Doing this allows one to use the pedal for other important purposes such as etching a melody, bringing out strategic harmonies, layering sound, and doing half and quarter pedal releases to spill excess overtones out of the mix. Even at that I probably use more pedal than you, as I prefer a wetter to a drier sound in general in romantic, late romantic and impressionistic music. I no longer play Baroque or Viennese Classical music, but when I did I was very sparing of the pedal, especially where Bach, for example, calls for a mostly nonlegato touch and sound. I also played Chopin's Etude 10/6 with virtually no pedal except for some touches in the coda. That was Chopin's whole intent in composing that etude. Yet I've heard renditions with pedal that throw a haze (or pall) over the entire piece. Of course, for the Impressionists, it would be nearly impossible to play their works without generous pedal. Sometimes Debussy and Ravel even use the direction "enveloped in the pedals".
In playing the black keys, a trick is not to play them from above, but rather close to the keys. That provides greater proximity and security, so less risk of a klinker. In conjunction with that, another good point is to ensure that you're sitting sufficiently close to the keyboard, which can also be accomplished by leaning forward. Slip-offs often occur toward the ends of the black keys nearest to you. Using flatter rather than arched fingers is helpful as well. Both flatter fingers and sitting or leaning a little closer ensure that more of the finger pads are in contact with those keys, thereby making slides and slips less likely. (Conversely, there are instances where we cleverly and deliberately execute a slide of a finger onto a natural key to avoid a change of fingers within the fingering scheme for the passage.)
Yes, trills, tremolos and rapid repeated notes executed by three fingers are more difficult on an upright than a grand piano. The reason is that the hammers strike the strings where the hammer shanks being nearly in a vertical rest position . In the grand, of course, the hammer shanks lie horizontally under the strings, so they get far more help from gravity on the fall to the hammer rest rail. Everyone who has played both types of instruments at one time or another notices that difference in the design of the piano actions and their resulting response during rapid repetitions. Also, when it comes to grands, the longer the piano, the longer the keys (including the invisible part behind the fall board). That extra length provides greater leverage to the pianist, thus enabling more control over touch and dynamics.
I had to chuckle at your experience with Baldwin.
Had you owned the Baldwin Model 6000 Concert Vertical, probably all of your neighbors would have had to evacuate the building! I play a Baldwin Model L Artist Grand (6'3" or 1.83 meters) which is a parlor grand, larger than the typical medium grand. And it's powerful! Fortunately the furnishings and carpeting in the living room help to absorb some of it. When I practice during warm weather, I close the doors and windows out of consideration for the neighbors even though they're not close by. There was a blindfold test a few years ago with some people in an auditorium listening to Steinway, Yamaha, and Baldwin concert grands on stage with the pianist playing the same piece on each. They all picked the Baldwin as having the the most robust sound.
I cannot memorize anymore, so after I record a piece I put it away and move on to the next one. Plus it's been a couple of years. But if you can give me the measure number in the Bortkiewicz 40/6, I'll be glad to dig it out and fool with it a bit at the piano to see how I executed that figure you mention. If you couldn't detect what I was doing from the recording, then that's a good thing!
Incidentally, I recorded that Prelude in the early summer of 2008. It was a hot day and the A/C was running. After I finished the recording, which I liked, I noticed on the out take that just before I started playing, I could hear the faint hiss of the A/C air leaving the ceiling defuser which was not that far from the microphones. It didn't spoil the recording, so I didn't bother to rerecord it, but the purity of sound would have been still better without it. So now I always shut off the system before a recording session no matter how hot it is! Live and learn.