Commenting on using Keyscape and Omnisphere: I use them in a live situation for sure, in single linked racks, and preload them. If there are good alternatives I use them (e.g. Pianoteq for acoustic pianos and CP80, and if I do not need the super strings in Omnisphere I take them from XPand2), but for EP’s I prefer Keyscape. As we know in our gigs what the next song is - we use pre-agreed setlists - I immediately switch to the next song in the list upon the last note of the song. Never had a problem with that. No delays, no latency.
It is wise to have at least a computer with 16Gb RAM, as preloading a few Omnisphere and Keyscape presets adds up. One trick is to use the 8 Omnisphere slots - assigning them to different midi channels - and switch Midi channel. That results in almost immediate loading. But preloading 8 presets adds up in RAM.
I actually revisited Waves Epiano 88 yesterday and must say I like it better than I thought, especially if you take some of the reverbs/effects off and replace them with - in my opinion - better ones. Still a difference between 29 and 350 (but Keyscape gives you much more different sounds, including a good Yamaha C7 acoustic piano, Wurlitzers, 2 Rhodes, and various others classic keyboards such as MKS). Especially during more quieter intro’s of songs for me it makes a difference to use Keyscape EPs. Sure, in a louder context, many other EP’s do as well.