HD rigs are no longer a necessity by far. That's just good advertising on Avid/Digi's part. A current computer running PT is just as fast and efficient. HD rigs were a huge thing back when the outboard DSP made a difference in performance. Like..."I'm running a Pentium 4 1.2ghz with 128mb Ram and with an HD rig, I can put a compressor on every track or run an advanced reverb plug without crashing my PC!!! Such POWER!!!!"
HD rigs are cool for working with outboard gear where sounds are constantly leaving and re-entering the digital realm, but that still falls on the hardware, and can be done with a rigged computer only version just as easily with the right outboard gear. Main reason why the no longer push an "LE version" and have got rid of limits they purposely put into place.
If you own a copy of Pro Tools 11 and are running on a computer with recommended specs, it's gonna run just as smoothly and flawlessly as any other software. My only gripe with PT/Avid/Digi is up until updating my Mac(OSX Mavericks)my copy of PTLE8 and M-Box worked perfectly, now to upgrade they want $399, the price of a completely new DAW and all I use it for is compatibility when receiving files to mix from other PT users.