The North/Duotone Rebel has very little in common with the Fysurfer Peak4. You would have a hard time finding more different kites and there can be no meaningful comparisons drawn from experience with one to the other.
I've used both the 5 and 4m Peak4s on 4 different bars over 15 sessions all on the same hydrofoil from 9 to 34 knots . All precicely trimmed with dry land flight testing. 17, 20, 22 and 27m lines, both high and low split, with and without trim cleat, standard chicken loop and slider set up without chickenloop, all single front line release safety.
17 years of experience in the sport. Have been rebuilding, trimming and maintaining bars since the beginning.
I can assure you unequivocally that you can get the absolute most out of your Peak4 with any properly trimmed 4 line bar.
There is a pretty short sheeting range on them. as with any other kite, slightly larger throw as you increase kite size, but for the 4 and 5m sizes it is vey similar to other kites with very small required sheeting throw such as BRM clouds. As such, no trim is required throuhout the kites range (10-20 knots on the 5m, 14-34 knots on the 4m), however, if you would like to ride the Peak4 unhooked, a trim cleat is advisable.
I'm sure the stock Flysurfer bar for this model is great. The finishing and though that has gone into the details on the kite are excellent and I am sure the same attention to detail has gone into the design and construction of the bar.
If you take the time to go back through this extensive thread you will find that Armin himself states that the Peak4 works just as well on any suitable 4 line bar trimmed to have all 4 lines the same length at full power, and that they work well with either high or low front line split and that both single front line release or the included B safe 5th line are appropriate, with on land re ride being the advantage to the B safe system.
If you insist in you opinion that flying the kites on a non stock bar will have a detrimental effect on kite performance, I invite you to test the assumption yourself and report your spicific findings.
Until then, the concensus among those that have experience with the kites, including the designer, is pretty clear.