Most people I have seen here (at least on ERGO or PP) say they really felt to shut down at the end of week 2 or 3.
And many accounts say they never really felt shut down on just SD.
So, assuming that it may take just over 2 weeks (and to me, PP or LMG definately add some sort of T to your system, while SD may do the same but not to the same extent as the others IMO) to fully shut down, ending as cycle right before would mean that your not totally shut down when you begin PCT.
As far as tring to keep your nat test going, it would be possible to keep it going (at least a LH signal) while ON cycle. Even if your body is getting it's T from another source, you can still be telling your body to produce. Im sure, that after the first 10 days or so, the amounts will be reduced some, but its always easier to start a warm engin then it is to start one thats been left in the cold.
Ya might want to add some sort of E-blocker before bed, because your getting test from an external source, so your estrogen levels will be elevated as well (this will happen anytime you use Trib).
If your loosing size and mass due to your body going through re-regulation and the catabolic effects, then eliminating the distance between "stop to Go" will reduce the time and the extreams your body might have to go through to get there.
Now, it would seem like the gains from SD are "stickier" then PP or LMG, so I would assume that has to do with either the chemicals involved (with SD not being such a "external test" source) or the degree of time (and the reactions to the adjustments being made) it takes to self regulate.
Again, this is more common sence to me. I could be wrong, and there is a greater chance that Im talking out of my ass.
I mean, (for say) your going to loose %30 of your SD gains, then your going to loose %30. Wether you put on 10 and loose 3 (by the way, I just picked the number 30 outta the air) or put on 6 and loose 2. Your body also has to acclimate itself to the added weight. It would seem like a 6 pound gain may be easier to adjust to then a 10+ lb gain.
Maybe- (maybe) having to adjust to the 6 pound gain would be easier and not as drastic in a mass change where the body just might except it more, and not try as hard to adjust, thus lessening the amount of post-cycle losses.
OK, so now I feel like I freakn have an ad for my very own supp in the back of Muscle and Fitness!!
But, with as much as Ive said, It cant all be wrong???