Cat?
 

Does a cat converter have anything to do with performance on this car?

a catylitic converter halps to make your exhaust cleaner, your exhaust will flow better without, rendering better performance

If it's blocked-up it will cause a definate exhaust flow restriction which you don't want. If you think you have a problem, I'd recommend one of the Magnaflow hi-performance cats. They do what a cat is supposed to do with low flow restriction, and help mellow out the sound of your car.

Cat Light comes every so often
 

Engine is "motor boating" on cold wet days, after start up. Some times the "CAT" light comes on.
Is this justa worn out Lamda / O2 sensor? Or is the CVat in need of replacement?

Do you check codes? your cat may be clogged, i say that because supra's run pretty rich in stock form

"CAT" light? That's new... Mind posting a picture of this light?

i was gonna say whats a cat light. but then i decided against be fearing there might be one! hmm were did i put that link for dash board lights.
http://www.toyotanation.com/forum/sh....php?t=262353&
i think i seen a better One pic example before.. maybe not tho.

Hmmmm CAT light let me check....... low coolant light, check engine, taillight blown, ABS, Blinkers, High Beam, TEMS. Hmmmmm nope no CAT light there. Coolant light kinda looks like a CAT but only just kinda.

Their is no cat light..

there is no spoon.