Dude you DEFINITELY want an upped stall converter, and the shift kit valve body upgrade - once you have driven an auto with a higher stall, you will never go back.
Basically when you boot it the revs build, but the car doesn't move (much) until the stall takeup point - so basically you can almost never get caught off boost.
However, if you never want to zoom off the lights there probably is no point - but then you wouldn't own a Skyline - you'd be better suited to a Commonwhore
But, I am going to wait to save up the full $2,500 to do the stall, shift kit and kevlar plate upgrade to make a 100% bulletproof trans
AND, if you're aiming for 250rwkw you WILL need to do this too - I hear the stock trans shits itself at a bit over 200rwkw.