As someone stuck with both nVidia and ATI cards, I'd vote against using NV-CONTROL. Detecting the RAM for different manufacturers via different methods sounds harder to maintain.
(--) fglrx(0): VideoRAM: 131072 kByte, Type: DDR SGRAM / SDRAM
In my opinion parsing of the log file is very unreliable and second you aren't 100% sure if the card drawing the opengl stuff is the same as this card. (a X session can be using multiple cards)
When using NV-CONTROL only for use on Nvidia cards you are 100% sure that the detected amount of VideoRam corresponds to the current card rendering the opengl stuff. (NV-CONTROL is a X api and you need to provide it with a X display and screen number; this is the same info you have somewhere in Wine) I prefer to use a generic way but that way doesn't exist. Doubt alexandre would accept a log file parse thing. Not even sure he would accept NV-CONTROL code either but think the chance is quite bigger that he does.
Roderick