you will not find anyone here thats using those guns, if you can write italian then go to apnea magizne forums...
But, from what i see from the pictures..Gimansub dentex has wider wings than pelagos. Thats makes it more stable while shooting and tracking in horizontal plane, more power transfered to the shaft because of the less recoil. The negative side, it may be little less mobile than pelagos. Another advantantage of dentex is it integrate the power bands to the body of the gun better than pelagos. Thats makes better power transform and accuracy, hovewer i belive change will not be very visible. Pelagos has better line release (i think), gimansub's one may caought the line alittle while spear travels. Gimansub has esthetical benefits, hence the cost is higher.
For guizzo vs Labrax, with little size of the gun and band/shaft config they should perform almost same. Practically Labrax is just smaller version of dentex on the other hand, guizzo has wider wings makes it more easier to track on the horizontal plane but not much necesarry in my opinion since the shaft/band config is "weaker" there will not be too much excess recoil...I see the videos of the TOTEMSUB and observed that pelagos has little kick/recoil during the shoot but probably Gimansub Dentex will have significantly lower recoil... Just check the photo below to see the shape of the dentex body...
By the way why you just don't use pelagos for BASS?