I like my specialized bg jett 143 as well and have riden and raced on it all summer...
The cutout is nice and wide, which in conjunction with the relatively flat rear platform of the saddle (as viewed from the rear) allows my perineum and labia to be completely suspended 'in air' between the contact points of my ischial tuberosities with the seat - zero pressure or burning. The rear of the seat is very firm but comfortable, with a slight flare up at the tail edge which gives the sensation of the seat pushing back when I am really driving the pedals hard and prevents the sensation of sliding off the back - a very powerful and energy efficient feel.

However, a few things don't quite 'sit well' with me about it...
The mid section of the saddle is a bit too boxy and flat before it tapers to the nose, which causes pressure at the origin of my hamstrings (ie. near the skin crease between each leg and buttock). The nose of the saddle is just too wide for my tastes, also. And I have found positioning the saddle very finicky - even the slightest mm's change in fore-aft, seatpost height, or tilt dramatically changes the overall feel from comfortable to very uncomfortable.

So, I just got the sella italia signo gel flow and took it out for a short spin/climb...
It has a rear width of 141mm - very close to the jett's 143mm, and it is only slightly longer nose-to-tail (<5mm longer). First, it has a cutout like the jett, but the opening is notable narrower. Second, the platform of the saddle is more curved than the jett (as viewed from the rear). Third, the rails of the saddle stay midline (instead of flairing to the back corners of the rear of the saddle like the jett) which gives the wings of the saddle notable flex on the pedal downstroke. These three things together brought my perineum and labia in closer contact with the saddle which definitely caused some midline pressure - however, my ride was not long enough to tell if that will generate pain or burning with longer rides. My first impression is that I don't like the wing flexiness, but again I need to give it more test time. The mid section curves more nicely to the nose, which was definitely more comfortable at the origin of my hamstrings, and I like the narrow nose. Finally, the gel is minimal so you still retain a comfortable firm feel.

In summary, the signo gel flow might be a good alternative for the jett 143. I'm interested to know others opinions of these two saddles. Also, what other cut-out saddles do you like (and dislike) if you like either the jett 143 or the signo gel flow?