The 650 is newer and the pads are kind of stiff. My 600s are about 8 years old and I replaced the pads, out of the gate the pads we much more pillowy. I use the 600s on my non-DAW only.
I prefer the 650s to the 598s in how they are both constructed and feel on my ears. Since both of mine were profiled by Sonarworks, the delivered sound isn't much different unless I just play them without Sonarworks enabled.
FWIW I keep a spare iLok on hand and I pay the $30 per year insurance so that if my iLok goes bad, is broken, lost or stolen, I can send in my spare and all my licenses will be transferred to the new iLok with overnight shipping both ways.
I've been a Kilohearts subscriber for over two years now. I've got $200 available in rewards (100 added every 12 month). 5 moths to go until I have $300.
I do already own Snap Heap and Multipass.
In order to own the full boat it will cost me $239 on sale with a catch. You can't use Rewards on sale prices. Bummer.
One more thought about Reaper, get the (independent) SWS Extensions (donation ware) and azslow3's ReaCWP Reaper plugin to open a CbB cwp file in Reaper to "pretty much" get your outstanding projects into Reaper format. I've only tested about 10 projects and have only had to make some very minor adjustments.
You can try all this today as Reaper installs as fully functioning demo from the download page.
The of the four choices you listed
If $80 were my budget I'd go with Reaper. V7 was just droped and a license is good for 2 versions (i.e. 7 and 8 right now) which traditionally is around two years.
Harrison is more like 18 month cycles between versions but the upgrade cost is not break the bank level (around $50 IIRC).