This may or may not be relevant to the problems you are having but I noticed a while ago that the way you have your tracks routed makes a HUGE difference to your ASIO meter and your ability to run high plugin counts. In a nutshell, if you have lots of complex Group channel routing with long plugin chains, your ASIO meter will be higher than if you just have lots of individual channels with the same plugins arranged in short chains.
I did some tests a while ago (this was with Cubase 7.5). I had a session with the exact same plugins (24 x Waves Kramer Master Tape) and the ASIO load ranged from 15% right up to 100% depending on how the tracks were routed.
#1. ASIO meter at 15%, Windows CPU at 15%
24 x stereo tracks, each with 1 instance of KMT, no group tracks.
#2. ASIO meter at 45%, Windows CPU at 11.5%
3 x Stereo tracks, each with 8 KMT instances, no group tracks.
#3. ASIO meter at 100%, Windows CPU at 11%
1 Stereo track, with 8 KMT’s, routed to two groups in series, each with 8 KMT’s. i.e. a continuous chain of 24 Kramer instances.