IIRC you have about a 7.55 SLR? Pretty weak? What are guys with similar combos running for Starting line ratios? I guess the real question is how much starting line torque they have. If converter multiplication is 2/1, then 7.55 x 775 x 2 is 11,700 ft lbs at the axle. I am curious what others running where you want to be have for that number. My deal is about 16,000 at the axle, and it hammers against the wheeliebars too hard, spins so bad you can feel the car loose traction, and still goes 1.28. My best is 1.261 I know I have issues that slow it down in the 60 ft, but feel eventually it should go at least a 1.24.
The thing that got my attention is the lack of any wheelie at all. Tells me you can probably use a lot more grunt off the line now, just need to control the rear axle for best results.
If you get a good converter that stalls say 6800, it might actually multiply torque a little less, combined with a tad less torque at the higher rpm, and unless the SLR is increased to the point where it gives you a fair amount of increase at launch, might not show the results it is capable off. Just my rambling thoughts, hope it gives you something to consider.