About physics:
It has been said, if you turn everything off except ABS 1, GT5 physics are still somehow nerfed. FACT IS: if you want full GT5 physics you need to turn EVERY assist OFF and accordingly adapt your driving style, braking skills, brake bias and car setup to ABS off.
About brake techniques:
Some people use a sponge ball on DGFT break pedal for more control. I'm not using it yet, for now I prefer run with 1/0 or 2/0 brake bias and softer suspensions, DFGT pedals has only 2 pedals so I'm not using proper heel and toe technique. I brake with left and blip throotle with right foot. The result is like heel and toe without heel and toe. Blip is needed to settle car inertia while entering the turn, at the same time it keeps engine revs high.
I tried to use only right foot on 2 pedals but my mind feel the need to use left foot for something so I use this alternative technique.
an other proof for me that abs in gt5 affects more than the braking is that it also change the behavior of the car when downshifting with a clutch. with abs on 1 the car does not seem to be affected by the amont of compression of the engine, without abs, the timing of the downshift is important to maintain stability.
These are two different things. In manual (sequential) or automatic mode, GT blips the throttle and matches the revs almost perfectly, so there is no need to blip the throttle for rev matching unless you're using the clutch.
The stabilising effect HKS racer is experiencing is well known, and was the topic of much talk in F1 a few years back when they were running those trick diffs, and more drivers started "left-foot braking". This was when the cars were running 900+ bhp and 20k+ rpm limits, so engine braking was phenomenal. The "left-foot braking" description was sometimes not useful for the discussion, which was actually about
overlapping the controls (throttle and brake together), not just which foot did what. Ironically, this practice of overlapping the controls had probably been going on for years beforehand, but the "switch" to left-foot braking in F1 brought it to more people's attention.
The reason you do it is to either reduce the engine braking effect (by bringing the net longitudinal thrust at the wheels closer to zero, i.e. "neutral throttle") or to take the diff out of its "deceleration mode". On deceleration, most road-car diffs are practically open. On the limit (braking and turning) this means the unloaded, inside wheel gets the majority of the "back torque" (engine braking effect) which causes the instability you're feeling - imagine pulling on a rope tied to only one of the rear wheels, the car will want to rotate more in the direction that it is already turning. The GTR, 458 and older F1 cars, as examples, constantly adjust their diffs to prevent both understeer and oversteer in all conditions, so that engine braking works favourably with the driver's intentions. I imagine GT5's ABS takes the engine braking into account so as not to lock wheels that have additional braking force from the engine. This means, when braking, the ABS handles instabilities from engine braking to some extent, so it would be less apparent, except in the extreme.
It's common to see
professional drivers trailing the throttle with their heel or the side of their foot when braking into a corner, even when they don't change gear. A
similar approach is useful for 4WD rally cars on loose surfaces, but that overlaps with
another technique that you use on FWD cars that changes the effective brake bias rearward to
induce oversteer, not prevent it.
So, you only need a very small amount of trailing throttle to stabilise a RWD car under braking, i.e. just enough to neutralise the throttle (hold a constant speed). Despite the diffs now being functionally limited, F1 cars still use this technique, possibly in the engine map with some headroom left for driver control, and I think they call it "back torque limiting", a term inherited from the motorcycle world, where engine braking is even more of an issue.
It's also important to remember that this is all heavily dependent on differential settings; front, rear and centre. In that sense, it helps to think of the individual forces at each wheel under different circumstances, but most drivers have an intuitive feel as to what control inputs work and what don't, even if they can't explain why.
also I don't rely on engine braking much (don't like it IRL either). Also I ease off the brake entering a turn. 
)
and its their preference to drive with ABS in time trials
