[squid-users] Still at 3.3.11... time to upgrade?

[Travel Factory S.r.l.]

I have to say that squid 3.3.11 worked flawlessy since january 2014...

... but I think it is time to upgrade.

My server is dated but it has 16 cores and 32 GB of ram, with less 
than 3000 users. Workload is split between 2 identical servers thanks 
to a proxy.pac.
I have spinning disks now but I also have a couple of SSD in the 
drawer, just in case they are now fully used.
O.S. is linux Red Hat 6.4.

Can you please suggest some docs to read about the migration path, the 
changes needed, the new features of 3.5?

Thanks