That's why you get demo's from an online retailer (TW, T-P, TE, etc.) then immediately cut the demo string and put in your benchmark poly at your preferred dynamic tension (DT). It may not be seen as completely kosher by some, but cutting the demo string is usually not a big deal, as they usually restrung every few shipments anyways.
Not on those models specifically, but I can offer a general predictive comparison, as I own the VCP 97 and 97D, and have plenty of hours on the G360+ Speed Pro, PS97 v13 and Blade v6, so I think I can extrapolate pretty well, knowing what changes have been made to each silo since the models I tried... That said, you didn't specify which model(s) of Percept you're interesting in comparing... I'll presume the 97 and 100 unless you say otherwise.
At equal strung spec (static/balance/SW) with the same string and dynamic tension (DT):
Power: P100 > SP >= PS97v14 = GP >= Bv8 >= P97
Spin -- mechanics can alter this, but generally: P100 > Bv8 = P97 >= PS97 > SP = GP
Control: PS97 = P97 >= Bv8 = SP = GP > P100
Feel (Raw to Muted): PS97 >= GP >= Bv8 >= SP = P97 >= P100
Flex (Firm to Soft): PS97 > P100 >> SP >= P97 >= GP >= Bv8
I'm sure there will be some corrective interpretation on the way I've ranked the above, but overall I hope it paints at least a somewhat helpful picture. In general, the frames you're comparing all that different from one another. That said, if you can expand more upon what you're looking for, we can probably help make a recommendation as to which exact Percept(s) to try.