Higher differentials generate more spin, higher launch angle, and easier on the arm. Starting low and working your way up you will find there is a loss of control at some point. For me playing Gut/poly that is somewhere around 4-5lbs that I lose control on the serve, return of serve, attacking the mid court ball and first volley. 2-3lbs is perfect for me in the RF97. Personal preference and different for many players.
So, the gut/poly tension difference question is a good one. I think that it surely depends on the feel that you want, and the cross string that you are using (more stiff, or more comfy).
Right now, I have settled at 58lbs mains (various), and 48lbs crosses (PRCW). That seems to work well for the moment. I got here by not wanting the poly to be higher than 48. And i kept increasing the gut to tame the power. Not sure i would go higher at this stage.
Oh, and I pre-stretch the PRCW (10% on my stringer's auto setting) to try and hold it at 48lbs for longer.
This is the reason we see a great number of people stringing gut/poly at the same tension. Lowering the overall tension to avoid the stiffness right off the stringer and the string bed plays better longer. Normally I string a 3lb differential but notice a difference going to even a 2lb differential in terms of string bed stiffness. If you want gut/poly to last longer string the same tension with a smooth poly with the best tension maintenance you can find. Then string mains and crosses at a lower tension.
Ex: RF97 57/54-59/56
Have a friend who plays Gut/poly at 52/52 in the RF and gets much more longevity than I do using differentials.
I got a Strike 18x20 to experiment with, the stringer strung it 52x51 (VS 1.25xALU 1.20). I usually use a 4# differential (52x48) but the stringer said that the new grommets would settle, so this would be better. 1st time out it felt like crap... seriously, bad enough that had i not purchased the racquet I'd probably not have hit with it again. Luckily, I tried it again after it sat for a few days and it felt great, and has for 10+ hours so far. I attributed the suckage to the string bed being locked up until the ALU lost some tension and created some differential, but what do I know? Is this 'break in' typical in no/low differential gut/poly setups? Does the longevity warrant the 'break in'?
I'm an old school Yonex guy so I always string the crosses 5% lower no matter what. Seems to work out especially well with gut/poly hybrids. The only time I've done a higher delta was with especially stiff poly, but I never do more than 5 lbs difference.
I've got 1 set of natural gut I'm itching try out the gut/poly hybrid in but I'm getting ready to move to a new racquet and want to try a multi/poly hybrid first in order to compare two different round and slick poly's in the crosses...before I try it with the natural gut.
Wilson Revolve is one I know I want to try because it's known to be smooth and allows the multi/gut main to do its thing without notching.
What should be my 2nd smooth poly string to try out in the crosses with multi mains?
Apologies, I posted this also in Poor Man's Champion's Choice:
I used to use KB Max Power smooth crosses with gut before I got my own string machine. A friend gave me his stringer and a few sets of AlLURough. And I hate to admit it, but it's really, really nice. I've seen some folks mention that they replace the crosses a few times before the gut gives out.
Just curious, with Max Power Rough would I maybe have to change the crosses a couple times vs the three or four times you would have to with the Alu Power Rough? I don't mind restrining, just want maximum playability. KB seems much stiffer and if the only benefit is longevity, it's not worth it. Or maybe a thinner gauge with the KB, or is there another string that is rough and in the middle of the Lux and KB?