Any one who intentionally attempts to fly with a trim tab disconnected is nuts. Twin Cessnas have history of trim tab issues. The Cessna 441 Conquest would up with a dual actuator on the elevator tab. This evolved from an inflight break up caused by the elevator trim tab problem.
Some of the model airplane inspired tabs and actuators found on EAB aircraft are scary just to look at.
I sincerely doubt that most pilots understand what a violent event flutter is and how little if any time there is to do anything about it.
Still total silence on the EAB airplanes that race at Reno way beyond Vne.
Glasair III Vne 335 statute, fastest Reno Glasair is doing well over 400 lap speeds.
I'll provide some feedback from the air race arena. Nothing said here is intended to infer that Vne doesn't apply to a built-per-plans aircraft, or that exceeding Vne is OK, just because racers (at any venue) achieve the speeds they do. Our class has RVs and Rockets of many varieties racing. We've had Rockets over the stock 275mph Vne, and some RVs over the 210mph (4/6) or 230mph (7/8) stock Vne (and I'm using TAS, as directed by Vans...which more closely matches lap speeds). The Super Legacy and Super Glasair aircraft have already been mentioned in the quoted post.
As many know, many racers are modified. Thicker skins on portions, thicker stringers in some locations, modified bracing, improved trim tab systems, layup strengthening measures in the empennage of the fast glass planes. We operate in a highly scrutinized environment, with waivered airspace and strict SOPs and Rules of Competition. In Reno, we must certify that we have tested to 105% of our qualifying speed. We are scrutinized on modifications, and on the test program we apply to our aircraft after making them.
As speeds have increased, whether though drag reduction or HP increase (via engine increases or boost/nitrous additions), we've increased the scrutiny. We pay attention, and dig into the modifications and testing. We are not cavalier about the process...or the speeds.
We've also modified our operational procedures, especially during the downhill chute start, to keep our pilots and aircraft from delving into what might be considered clearly dangerous territory. For RVs in the Medallion heat, we come down the chute at 150 KIAS (that's about 190 MTAS, or 20-40 mph below stock RV Vne, depending on RV type), with a flat trajectory, and to a release point closer to the start pylon, to keep the speed in check. This provides a better margin, with less time for racers to be at full power while descending onto the course. In the end the pilot also has control over his or her speed with stick and throttle. Speeds for our other heats are selected with the same safety margin in mind. Rockets in the Bronze see about 170 KIAS in the chute prior to release.
Bottom line, in answer to the above question, is that the speeds in racing are not attempted without modification, testing, tech inspecting and review. If we have potentially unmodified aircraft pushing into high speed regimes with bolt-on HP mods, we scrutinize and counsel. Could a modified aircraft be considered to have a modified Vne? Probably a debate that could rage between manufacturer, builder, modifier, and pilots at large. The racing community has a long history of exploring the envelope...sometimes safely, with technological leaps sometimes being the result, and unfortunately sometimes not as safely. In a large air race meeting today, as a matter of fact, we discussed just this (modifications, testing, speed, and safety), and the emphasis is on safety. We owe it to the aviation event spectators to do the due diligence to ensure our racing is a safe as possible.
This post doesn't answer the OPs question either. One item I'll add, that may help there, is my story about being squeezed on a picnic bench during my first AirVenture Cup dinner, between Dave A and John H, probably the fastest RV drivers at the time, and still among them now. They trapped me there, and asked me "when are you putting a counterbalanced rudder on that plane". John had an -8, and Dave has a counterbalance rudder on his -4. They were being great mentors. Mine's a -6, built as a side-by-side Rocket (from the ground up, lots of mods) with a 540, and a Vne of 275mph. While most HR-IIs have a -4 tail, and a 275mph Vne, they talked to me about margin. I listened, and built and installed an -8 VS and rudder, with additional mods bounced off a (very) RV-knowledgable engineer. I still apply the Rocket Vne, but feel we added margin. This (the rudder counterbalance) may be one part of the answer to the OPs question, and would make sense (at least to me).
One last item I'll touch on is the disconnected trim tab test idea. FWIW, we had a Rocket flutter in the chute, when the trim tab attachment failed. A flaw in the trim tab control attachment that caused departure of the trim tab control horn...and the connected clevis...was discovered post-event. The event ended well, but did considerable damage to the elevator skins. Incorrect chute speed (too fast) resulting in a Vne exceedance (of about 10%) after race start was a factor as well. We don't know if the part failure or the flutter occurred first or simultaneously, but this may be an event to consider if one was considering testing with a disconnected tab. That seems more of a concept for the theorists to consider, than one for the test pilots to attempt (IMHO).
Last FWIW: one of my racing goals...to show mindset...is to do a level qual lap
at my Vne. Another is to fly a Corsair on the course. One may be more achievable than the other!
Cheers,
Bob