limitation didn't say anything about WebPack versus 'for pay'.
I remember something about ISE v10.1-v14.7, anyway I can confirm you that there is an huge difference between the WEBPack and the FULL license version.
We have a couple of copies at work, they don't have any limitation on usable threads, and the same software on the hardware with the same project gives you results in different times and it depends on having the license enabled/disabled.
Last time I wanted to check:
License Valid & License Enabled -> extremely fast on large projects, no matter how much complex the project goes
No license | no Valid License | License Disabled -> time results depend on the project's complexity
a) -> largely slow on large projects!
b) -> lightly slow on simple small projects (<1000 lines)!
Sonata Simili and Sigasi have the same behavior: the free license is limited and slower by several orders of magnitude when the project is large and doesn't use threads.
We don't use Vivado
By the way, consider yourself "lucky" of having the free WebPack, some UNIX solutions don't come with any free version and you have to pay for the license, otherwise the program doesn't run at all. Oh, and the licence is something like 20-50K euro per year!
edit: p.s.
on old Altera tools there was a trick: if you agreed with "I want to give statistic(1) back to Altera" they give you a bonus acceleration. It is an hidden button to be clicked and a some lines to read and to agree. I don't remember precisely where what etc.
(1) I just remember that it was like: which chip you mainly use? how many lines of code? VHDL or VERILOG? which is the used simulator? External? Internal? how many magic functions got used? how many IP? which IP? etc ...