Funny you should mention the Keylab 61.
My faithful old Novation Impulse 61 (bought in 2013) started acting weird and after trying a number of things, I decided to retire it.
I tried a NI 61A keyboard but it was too clacky/noisy for me so I sent it back.
I ordered a black Keylab 61 mkII from Vintage King (couldn't find anyone who had any in stock).
That was the beginning of July and my sales rep said my order was added to an existing order that was made in June.
So far, no word on when I can expect it.
Luckily my Impulse still works well enough so some workarounds make it useable for the time being (I do have to unplug it when using some Kontakt instruments that use CC#1/mod wheel for important controls such as dynamic layer choice).
Anywho, I'll let you know what I think when it gets here.
Regarding softsynths,..
They vary greatly. But newer ones aren't as cpu hungry as ones like Omnisphere or Stylus.
I think that modern computers have plenty of grunt to run any standalone synth though.
Of course, certain patches are worse than others (complex time based modulations) and you can bring just about any cpu to it's knees if you stack enough of them.
When I was in between houses and staying in an AirBB, I ran Pro Tools, Ableton, Logic or Reaper from my 2012 MacBook Pro in clamshell mode (closed with and external monitor).
It has a 4 core Intel i7 with 16G ram.
Here's a screenshot of a Reaper session I was working on at that time.
Not exactly a big project but I can't recall even thinking that it was putting a stain on my laptop (the laptop's fan noise makes it obvious when it is having a tough time).