There is a whole science behind this. When running a LOCK UP torque convertor and will NOT be locking it a WOT then you need to get the tightest convertor you can to meet your needs.
Alot of hype into smaller convertors to gain less rotating weight,this is tru that the loss is a gain.
If it is a lock up convertor and its smaller in size (say 10"for example) the area inside the torque convertor has to have a set amount of space for the lock clutch and components.
With that said, the remaining room for the turbine and stator is less fin surface area to grab the fluid hyrdaulically to try and couple than when compared to the stock 12" style d5.
So just buying say a 2800 or 3k stall 10" L/U convertor to help with launches, or spool the turbo is going to show its ugly face in 2nd and third gear if its not set up properly and ineffiecient...what do I mean?
The above brief jist on the smaller sized convertor losing fin area to cut into the fluid shows up as slippage when the gear multiplication goes down as you shift from first, to second.......less help from gears and then finally......3 rd which is one to one ratio.
By the time you are in 3rd the car is laying on the slop in the convertor and slipping if you will.
Im not a fan of forcing L/U at WOT as its hard on the trans parts and torque convertor clutch.
There is L/U convertors (presicion industries vigilante) with multi disks that are designed o handle the abuse. But they require and pump mod, have a tendency to rattle at idle and may stall the engine when put in to gear when cold.
Other option is to go non L/U and give up 250- 300 rpms vs the lock up.
Con with the non L/U is more heat is produced and the gas mileage will drop a bit.
If your are going to stick with the 12" D5 thats restalled then 2800 is it for stall over that and its just a turd and will lay over since the fin angles inside the convertor are tweaked to get more stall and the downside is slippage in higher gears when unlocked at WOT as mentioned
PTC, Pro Torque, Pats are all good convertors just get it tight/just enough to get by if going with L/U.
Call around and ask them about unlocked efficiency.
Went a bit overboard on explaining but have but I have made the mistake and bought the higher stall for what I thought was helping and the car lost 7 mph and 5 tenths in the 1/4 with a sloppy convertor. It would spool the turbo like a beast just sucked in its coupling ability.