Lujo, I don't see how you are consistently getting Enlightenment from GG and still being able to reliably convert out. I usually don't even come close. I think it's doable if you find any early Halpmeh and 'milk' a serpent for its venom, but that doesn't happen every time, or even most of the time.
You can do it rather easily if you have the Agnostic's Collar and a third altar. I think the benefits of Enlightenment are better than having a third option to convert to after draining TT of useful boons.
I've become a big fan of the 2nd level absolution. It gives you somewhere around ~25 HP and at most only removes 10 xp of monsters from the game. The extra HP at 2nd level are HUGE and let you reliably challenge 4th or even 5th level monsters right out of the gate. Combined with Humility, that's a huge purse of extra xp. I like this better than a late game absolution, which gives you massive hp but makes it hard to refill them, which defeats the purpose.
You would think that you would miss having ten extra popcorn monsters around after converting to TT, but you really don't. With Tikki's edge, I find that I can still consistently hit level 9 (with humility, so really level ten) before killing the boss, and level 10 (really 11) is not uncommon. As for the ~50 piety or so I could have gotten by forgoing absolution, eh, I don't need it. I'm ending my games with all of TT's useful boons already bought and still swimming in piety.
I haven't tried starting with TT yet. I think the way to go would be to enter with 50 gold, find 5 more gold in the dungeon, and then buy Poison and Tikki's Edge right off the bat. You can't really use GG at all if you do this. Your late game options are either to just stick with TT (he doesn't have much else to give you at this point, but at least he leaves you alone) or maybe convert to Taurog for an extra 15% resistance.