@savingclassicmotorcycles I've owned 48 Triumphs and only 21 Nortons, so the numbers MIGHT tend to show which one I favor. BUT, the numbers don't ALWAYS tell the whole story.
I'm CHEAP, and in my lifetime, I've run across more good deals on Triumphs than I have Nortons. BUT, THAT doesn't tell the WHOLE story.
I had owned 12 Triumphs before I bought my first Norton, an original '75 MkIII Interstate. By that time, I was solidly in love with the Bonnevilles, I think 9 of the 12 Triumphs that I owned by that time were Bonnies.
Once I got familiar with the Commando, it became my "go-to" for ALMOST ALL highway riding. There is ALMOST no comparison; BUT, that doesn't tell the whole story! The MkIII is an 850, the Bonnies were mostly 650s and (2) 750s. Even a 750 Bonnie is no match for an 850 Commando except in tight, light stuff.
When it came time to decide what to build to go vintage roadracing (2007), I picked a 650 Bonneville because I had overhauled and restored many of them, and very few Commandos (I think over a dozen Triumphs and only 3 Nortons at that stage). So, confidence and familiarity figured into it, more than raw capability; I wanted it to be bulletproof.
Catching back up to today, 2025, I have put MANY hundreds, perhaps thousands more miles on classic Triumph big twins than I will ever put on Commandos, but not necessarily because they are the "best", "fastest", "coolest", or any other reason; rather it has just become PERSONAL PREFERENCE. Even then, of late, I have fallen into REALLY digging the modern (early 2000s) Triumph triple 900s. I have 3-4/5 of them, and they are really great performers while still being light enough not to be "potatoes".
Back to your original question regarding 70MPH touring (vs an 650SS), I've not owned a Featherbed 650 apart from my 650SS-framed Triton which actually has a 750 top end. I've not done ANY serious highway miles on it, that's not what it was built for.
OTHERWISE, I've had so much fun in the Texas Hill Country on my 650s, mainly because apart from a few choice sections with either long straights and/or wide sweepers, I never hold them to cruising at 70+ (not that they couldn't). They are absolutely brilliant at all-around riding, and I even used my '70 Bonnie to do one of my 100/100/100 rides, and it happily did the ton without complaint or overheating.
As far as my race bike, a '65/66/67/68/69/70 Bonnie 650+.020 scratch built stocker (electronic ignition), it only failed me twice over 4 years, 33 road races, and a pass down the Bonneville salt: once, when a muffler rattled loose on the last lap of a race (Barber's), and once when a coil wire connection grounded out on the gas tank, also on the last lap (Willow Springs). Otherwise, after my first 2 race weekends as a rank rookie, I was NEVER beaten to turn 1, always being gridded on the last row, and even against 750 triples and 4s (the class is over 500 to 750cc). I placed 5th out of 22 riders in class, racing only 1/2 of the available races in 2008. I AM NOWHERE NEAR AN EXPERT RIDER. I credit the BONNIE for that record.
It has quickness, lightness, durability, plenty of speed, and RELIABILITY (if properly fettled).
The 500 twin is also great, BUT NO MATCH FOR THE 650, especially on extended highway use.
As for single carb vs dual, I never owned a single-carb 650, but I ride a good few and restored a couple. Anywhere at highway speed and above, is right where you want that 2nd carb.
I hope this helps you make your decision...
