I believe it would be better if you test rode them both and decide.
I own a Kawasaki and Suzuki therefore, am impartial to the brands, but not those models, only in-line fours.
From the technical point of view, a 90 degree twin is naturally smooth, whereas a vertical twin is not and need the help of balancers to smooth it out beyond 500 cc. , for that reason, I'd prefer the SV purely for technical reasons.
.....if carrying a passengers, torque becomes more important, and probaly I'd look for something bigger.
Thank you! My plan is to buy a bike that 90% of the time I’d ride solo. But every now and then if my wife wants to come for a cruise she can. Ride that bike for a few years then upgrade to a bigger cruiser or ADV.
But if I could get a bike that we can both ride that would be best.
You could also look at the older Kawi ZR7S models. I have one and use it for daily commuting, occasional 2 up riding, and both day long and multi day longer distance trips. I do have it setup with extra luggage etc. The plus side is they are not overly expensive to insure or maintain yourself. Being air/oil cooled & carburated they are fairly bulletproof and don't have an obscene amount of HP. Unfortunately I can't compare them to the other bikes you mentioned.
I agree with Obo said about the ZR7.....I own a '90 Zephyr, the predecessor of the ZR7.
Of course, ...no ZR7 are available new since 2006 or so. The ZR7 was same old '78 KZ750 refined, pressed into service against the SV650 as stop gap, until Kawasaki could developed the Versys 650.
.....but all these bikes, ZR7, SV650, and Z650 are less than 500 lbs. You are 230 lbs, with a passenger, we are talking about at least 450 lbs load. I totally agree with Obo again about 'obscene" power. I own a Suzuki GSX-S1000, and even though great, fast, and 'exiting', the '90 Zephyr is EASIER to ride,...and a lot, ..a lot..EASIER to service....no computer, no sensors, no liquid cooling, no complications, and is completely naked, you can see everything.
....this is to say when it comes motorcycles, is best getting exactly what you need in power and weight, NO MORE.... I am only 117 lbs, and 500 lbs is my limit of what I can wrestle on the ground or pick up, if I drop it.....and in the US about 500 cc is really all is needed for solo riding. Is agile, fun, and still accelerates quicker than most cars.
...I'd say all these bikes ZR7, Z650, SV650, and would also add the Yamaha FZ7, are great middle weight bikes for solo riding...no more is needed. I'd simply be a bit concerned if carrying a passenger for long distances, and also vibration from the vertical twins. I used to own a FZ-09 triple, and for me, it had horrible vibration at certain RPMs in spite of the balancing shaft....it had to go.
Those are both great bikes, for solo riding. Sv usually has more character as do most vtwins. Z650 is probably the easiest bike out there to ride. Ive ridden both.
Either will struggle 2 up though and get blown around on interstate due to lightweight.
I'm 6'2"/175 and both of those are a bit small. Fun, but small.
I currently have a ninja 1000 and although a little buzzy it is much more suitable for 2 up and interstate cruising. They also don't hold value and can be found rather cheap, which is a bit sad because they are great bikes. Not as powerful as zx10 so don't let the 1000 size be a concern.
Hope that helps.
My recommendations are always towards 1000cc or larger. That's just me maybe but riding my two brothers Kawasaki Vulcan 650 and Honda 750 Night Hawk vs my Ninja 1000 or my BMW S1000XR and there is no comparison to the fun factor. The big difference is the torque difference, as well as the HP, but more important the torque which makes it easier to ride slower and such.
PS my first bike ever was a Yamaha FZ1 and it is still one of my favorite bikes (also a 1000cc engine).
I sat on the z650 and was a little cramped. There are a couple leftover 2018 Z900 that might be a better fit. The sv650 I sat on was the model with clip on handle bars and I was too crouched over. Definitely want to be more upright.