I think you should plan on two rounds of demos, with the first being a more diverse group than you have. Those three frames are all 100 sq inch, 315g, and 16x19. That seems like a good second round of demos to try if you found that you like that spec. Your first suggestion of demos is more diverse and better for a first round than the second.
Think about beer. If you asked what kind of beer you should try and people gave you a list of three IPAs it would not be representative. You should try an IPA, a porter or stout, a pilsner and some crazy belgian thing.
I would suggest getting one - maybe two of those, and then some that are different. Heavier, denser, something with a spin pattern, etc... I would also try something from Head or Volkl just to see if
you like that grip shape better.
The new Pure Drives are coming out in a couple weeks, so if you are wanting the newest of those you should wait to demo.
1. Pure Drive or VCORE Si 100(stiffer 100)
2. Yonex AI 98 or Prince Tour 98 (softer 98)
3. Graphene Speed Pro or Blade 98 (for the 18x20)
4. Something different:
- Prince Tour 100T ESP for the open
- Something extended - A babolat or Prince Longbody
- Something demanding - Volkl PB 10 mid, Prince Tour 95, Pro Kennex Redondo 98
You are just starting this process. You need to try some crazy different racquets in the first demo so you can have an idea of the VAST range of frames there are out there. Two of them you will probably hit with for less than 5 minutes and think 'what the hell was that?' That's fine. Pick them up again after a few days. THEN come back and say "I liked the Pure Drive - what else should I demo" and then get another demo pack with the Pure Drive and 3 other similar racquets. You might surprise yourself and all of us and decide you have much better results with a much more control oriented frame, or you may find that you really like a soft frame and want a second round of the most arm friendly ones out there.
Don't get a demo box of Pure Drive wannabees until you find out you like that spec.