I dunno, i've had this debate with myself for years. I always remember some key factors when making such decisions.
Look around at any consistent 11 second trucks, and how many have been on their 700's for a relatively long time with no problems? My first truck lasted maybe 30-50 11 second blasts. It was tired when I was done with it, and the tranny guy that opened it up was amazed it still drove. I think the story is the same for most relatively fast Syty's. Tony's truck is having tranny problems. Nolan's truck is having tranny issues. Those trucks have been beat upon for tuning & some racing.. but it's hardly been more than a season's worth. For them... a rebuild or two every season may work out fine. It may get too expensive too, who knows.
The 700 has been into the 10s.... but every consistent 10 second truck I know of, has broken multiple 700's at that level, and most owners are looking to try new trannies & trans buildups to make 'em live at that level longer. There was never any magic number of 10.50 or anything... they were just liquidated in short time. I remember a couple of years ago at the Nats and Hoover was off a bit... and he complained about poor shifts in his tranny that were costing him some time. Sure the tranny was still together, but his performance was poor (relatively speaking).
I hate to see people be guinea pigs... the 700 doesn't even do well at 10 second levels for F body & Vette guys. There are a handful, but typically those are stripped down, lighter, 1/4 mile racers. Most go to 400's, 350's, some are going to the 200r4 even, as it has some billet parts available. There are many more of these type of racers than Syty people, meaning the money is there to test & try out new parts... and those guys won't even sticking with the 700 (for the most part). Once they make the swap, they get some consistency, and can stop worrying about driveline issues for a bit. I've seen a couple turbo 400's behind several 1000rwhp Supra motors... with the right build, they don't miss a beat, and can be absolutely tortured. The local shop will warranty them for 3 years at this build stage. The prices are comparable to a mildly built 700, and trans brakes & lockup converters are available.
It might be worth looking into doing a turbo 400, then swapping to 3.08 gears, and see if there is a lower 1st gear for the 400. This might make the 3.08 gears liveable, while giving you more speed into 3rd gear. This buildup would be best in a high powered truck that sees some street use, and has a relatively fast spooling turbo (to bring the boost up for 1st gear launches). Check out what some fast Buicks run... they have a 200r4, without the low gearing of the 700 in first gear, they have 3.42 gearing out back.. and then some step up to 28" tall tires. Someone do the math... the 3.08 gearing might be a *little* steeper, but it still could work out well. If I had a fast syty, chances are i'd either be doing this, or the 4L80E setup.
I guess it is all about sacrifices... what are you willing to give up? Run the 700, and bring a trailer & spare trannies (and your Visa or mastercard

)... Run a 400 and lose OD..... or try one of the other combos. Mike Lee sells a completely bolt in 350 that is pretty stout. That is probably the cheapest strong tranny combo I know of... no need to change driveshafts, mounts or anything. That route.. you could sell the 700 to fund the 350 purchase, or go back to the 700 if you couldn't do without the OD. Or try the 350 and if you couldn't stand losing the OD, try the 3.08 gears with it later.