Larry,
Here is some info that I gathered when making my trans selection.
Using the venerable Muncie M22 as the bench mark, here are the numbers.
The muncie has a 2.20 first gear. when coupled with a 3.54 rear gear, this gives an effective gear ratio of 7.79.
The TH 400 has a first gear of 2.48 which gives an effective ratio of 8.77, or the same as if you had a 3.90 gear.
The 700R4 and 4L60 trans both have a 3.06 first gear which would give an effective ratio of 10.83, or the same as if you had a 4.92 rear gear!
This right here explains why so many people run a 700R4 0r 4L60E on thier street cars. The low gear grunt that you get with one of these trans, is beyond compare. Keep in mind that both of these transmissions are of an overdrive type which drops your RPM to 70% of what the TH400 would give at highway speeds. Also, the 700R4 and 4L60E transmissions are both lockup type trans, where the torque converter is locked solid at high speeds. Both of the issues can substantially improve both economy and sound levels on the road. The only difference in the 700 and the 4L60 trans is that the 4L60E has computer controlled shift points, while the 700's shifting is controlled by a cable from the throttle position. Both of them are electronically controlled on the torque converter lock-up, but the circut to do this is very simple. You can controll the lock-up manually with a switch, or there are several vendors that offer a black-box to perform the task for you. I would not go to a 2500 stall converter, but would stay with a stock stall range converter. I have a neighbor who just recently put a 2500 stall converter in his car, and it drives him to drink at low speeds! The car idles down the street at almost 2000 RPM.
With this low a first gear and the torque of the bigblock, you will be able to shred tires at the blip of the throttle, even with the stock converter.
Now for the bad.
The 700R4 and the 4L60E trans have some weak spots in the stock form. Both of these trans are only good to about 350 ft/lbs of torque according to GM. A steady diet of more than this will really decrease the life of the trans. that being said, the aftermarket has responded with fixes for all the weaknesses of both transmissions. GM has also released a new trans, the 4L65E which has been beefed up to take the torque of the new LS@ engine in the Corvette, SSR, and GTO. This trans will take a regular diet of 425 ft/lbs of torque without complaining. This is the trans that I am using on the 65 with it's LS2 engine. You should be able to get a real strong 700 for about $2500, and can buy the new 4L65E trans from GM for about $1900. The aftermarket has come up with modifications that will allow these transmissions to withstand well over 500 ft/lbs of torque on a regular basis and never even flinch.
I think that an overdrive trans with a lock-up converters and stock stall speed, will make you one very happy camper! Fighting a high stall speed, high highway rpm's, and poor economy will suck some of the fun right out of driving the car on a regular basis. I think the lower gear ratio in first will more than make up for any thing you lose in the high stall.
Regards, John McGraw
The dry sump works fine on the street. No problems at all except for the whats that big tank for question that never goes away.:L 
