Hey ws5580,
The Gp2 is stronger in comparison to the GP2. It offers more backend strength then any particle as of date. My Animal (sanded to 400) can read a little quicker but is smoother in the backend. Overall, the GP2 OOB can still handle more oil with a strong finish as well.
Inverted1, with your pap of 5 1/4 and 1/4 down, I'd go with a 4.75-5 pin and 4.5-4.75 mb with the pin about 2.75-3 above midline. This should give you good length and a very strong backend finish. In regards to your 3x5 question, if the mb is in line with pin and cg, that would place it near to or left of thumb which causes for extreme length and not a lot of finish (arc layout). Since you're track is inverted, I'd also recommend not to place your mb too close to pap (under 3.5) because you shouldn't normally have much trouble getting the ball into a roll. Be careful with your mb 2 inches right of thumb idea because your pap sits under the mid line and that may push it a little close to an earlier roll layout. With the longer mb placement, we want to help create some length so it can store more energy for the backend. Hope this helps or feel free to pm me and I can explain in more detail, thanks.
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Rick Leong
Ten Pins Pro Shop
Track Intl. - Amateur/Pro Shop Staff
Vise Inserts Staff