I would still bank on the phase 3 or even 2 being the fastest production 4 door sedan in the world. The 426 Coronet would be a rival for sure but they only sold 2 and I would think that they would Weight a little more then the Falcon. Even though they had more HP and Torque under rated like the HO, they only made 2and they were not a production model and they were made in 66. There were a few American cars that would go close eg big block GM, Ford And Mopars and the E49 VH sedans but nothing that I would bet my life on. Maybe I am just a patriotic Aussie, cheers Aaron.
Being the "fastest 4-door sedan" is not really a massive claim. No-one really did this. GMH never built a production HK sedan with a GTS327 engine, or a HT-HG sedan with a GTS350 engine. In the USA in 1966-1969 the Street Hemi was available across the model range as a valid production option on Dodge and Plymouth, the fact only two were made in 1969 doesn't mean they weren't production cars, it just means very few people wanted one. The two 426 street Hemi powered 1969 Coronets were valid production cars as were the 3-4 1966-68 versions, one of them sold recently for over half a million $US. Dodge and Plymouth HAD to offer them in production cars so the engines qualified for race duty, which makes them little different to a GT-HO in that respect. The earlier 1965 versions of 426 Hemi optioned vehicles were proper race engines with 12.5:1 compression, but as far as I am aware no 4 door sedans built with these. The 1966-1969 street Hemi was the same engine but with lower compression of 10.25:1. There are various tests of stock versions of these, below is one from Car and Driver but it is a manual car with 3.54:1 rear axle:
1/4 mile 13.8s @ 104mph
Top speed 130mph
From what I've been able to find the auto cars (with 3.23:1 rear axle I believe) were mid 14 second quarters (various sources show 14.2-14.5s) but higher top speed.
The most reliable tests of Aussie stuff I have found are as follows.
Sports Car World December 1969 tested a properly tuned GT-HO. They did not like the car as a road car, said it was clearly built for one purpose, and you'd be better off with a GT or a GTS350 as both were far better road cars. It gets damn close to the street Hemi Coronet. People will tell you the PhaseII and PhaseIII as standard cars were a lot quicker, but this tells a different story. Also look at the fastest lap, fastest qualifying lap and total race time for 1969 Bathurst vs 1970. The GT-HO was faster in all than the PhaseII and 1969 had a fair few laps of slow speed at the top of the hill after Bill Brown's smash.
1/4 mile 14.8s average, fastest 14.4s.
Top speed 128mph.
Wheels October 1971 tested a well tuned PhaseIII.
1/4 mile 14.7s fastest (no trap speed). They got a run of 14.8 and 14.7 quarters once they figured out the way to do it without wheel spin. They also say it was slightly quicker than the PhaseII.
No top speed provided but they extrapolate it would do 144mph if it could run to 6700rpm in top. In theory it should have done 132mph at the 6150rpm rev limit. They do not say it did this though.
Wheels December 1970, Mel Nichols got to test a properly tuned HG GTS350. They only got the 0-100mph and top speed tests done, which were published as below. When they got the car same back for a second run to do the acceleration and 1/4 mile times it had been "adjusted" to perform like the earlier press test cars, it would not rev past 5500rpm and back to doing near 20s 0-100mph times.
Top speed 130mph+
AMC magazine tested a 38,000mile untouched HG GTS350 in issue 51. The car was properly tuned and tested just like the original tests (full tank of fuel, two people and throttle lift shifts).
1/4 mile 14.78s @ 95mph
No top speed recorded.
Racing car news, September 1968 tested a private, properly tuned standard GTS327 (with 3.36 rear axle). He saw through the Surfers Paradise Press drive cover up of the car's true performance so got a private car to test.
1/4 mile 15.4s (best) @92mph.
Top speed 128.5mph.
The SLR5000 and SS 5.0L tests are hard to find, and as I said they had tiny little 1 5/8" tailpipes which if you work out the total X-section are only marginally better for the pair than a single 2" tailpipe on a standard Holden (2 x 1 5/8" pipes have 2 x 2.074sq inch, single 2" pipe has 3.142sq inch). The first thing anyone did back then was replace the 1 7/8" mufflers and on a Torana put 2" tailpipes on. So even with the 250hp HJ 308 they were still restricted, and throw in a 2.78 rear axle (whereas a Holden with 5.0L manual and M21 4spd got a 3.36 rear axle and 14" tyres) and the Torana was hampered a bit even though it was lighter. Plus most LH tests are the early cars with the less powerful HQ engine.
Peter Robinson does give some insight in Wheels in July 1976, where they test a 5.0L manual SS. They manage as below. What the article does say though is "GMH's 5.0L V8 has enough power to give SS more performance than and other locally built car. In fact, it's so strong our performance figures had us comparing them to the old muscle cars".
1/4 mile 15.6s (fastest), 15.7 average
Top speed 188km/h.
I suspect that if this LX SS had been optioned with a 3.08 rear axle that it would probably get close to matching Rob Luck's GTS327 test, or going even better. Certainly if the tailpipes were modded as described above. However that is the case with any of them, option a PhaseIII w with a 3.5 rear axle or a GTS350 with 3.55 or 3.73 rear end and they'd go even better again.
In the end the Mercedes 300 SEL 6.3L was probably faster than any of these bar the Coronets, see link where there are some 1968 press tests quoted: https://en.wikipedia...enz_300_SEL_6.3
And certainly the 1975 450SEL 6.9L with its factory rated top speed of 140mph trumps them all again, see here: https://en.wikipedia...Benz_450SEL_6.9