Smallish, but totally usable. =)
Oh yeah, to expand on the touch screen functions of SSFIV 3D during battle, you have a couple options: Lite or Pro. On the touch screen you have 4 quadrants to touch (numbered 1-4) that activate a particular move or combination of buttons, similar to the Bleach fighting games on the DS. In Lite mode, you can set your "macros" to whatever move or button you want. For example, you can set Ryu's options to 1 - Shinkuu Hadoken, 2 - EX Tatsu, 3 - Focus Attack, 4 - Jab Shoryu. They're all color coded as well, so you have a visual representation of the type of move you've assigned. In regards to execution speed, moves come out as fast as the game allows you to input and can basically allow you to perform stuff that normally the computer would do, such as walk up sonic booms/scissor kicks/flash kicks/nightmare boosters/final atomic busters, etc. So if you're a struggling Guile player or someone who just wants a distinct advantage, Lite mode is what you want. Also, you can set your macros for each character in the game if you set your Lite mode to custom.
In pro mode, it only allows you to do buttons and button combinations, such as PP or PPP, etc., but no directional motions are available. It still falls in line with the 4 quadrant system.
Altogether, its a pretty robust customizable system and can be very useful to everyone playing the game.