Perhaps I worded it strange, but I was eluding to the V6 converter being more enjoyable to drive due to the higher stall in any combo. I've even put an I6 converter behind an LQ9, it's always more fun (imo)
It gets a bit muddiier post gmt400 while and this is kinda off topic: but at some point, GM "upgraded" all 4l60e's to 4l65E specs. not sure when this occured, but a 2007 will certainly have a trans equivalent to a 4l65E, no matter what it is designated. Electrically, they are the same I believe the only change was in the planetary, not sure if any clutches were even changed.
a 99 gen 3 (5.3/4.8) transmission will be upgraded over a 1999 Gen 2 V8/V6 transmission in the form of an additional 3/4 clutch. the input shaft is also different on ALL Gen 3 transmissions, not really an upgrade just a change. All design and internal changes aside, here is something I have found to be factual: ALL 4l60E's from 1998+ with the green plug are electrically compatible. I helped install a 1999 OBS suburban trans (with the upper hole) in an 04 Silverado with a 5.3, it worked fine afterwards. You need a converter snout spacer to make a gen 2 trans work behind a gen 3, which implies that this transmission still had the 298mm input shaft despite having the upper hole.
TLDR; it will work as intended (albiet will likely be weaker, if it is a stock trans)
This sheet should help you compare what parts are in what trans: http://mmerlinn.com/catalog/lilscribbs77/gm_9l6/gm9l6010.htm
yes, the 5.7 has much more low end grunt than a 5.3 but it will still work fine, and I would not say the V6 converter would be a 'bad' Idea behind an L31 or similar.
I'd absolutely recommend a trans cooler though.
