Craig_UK, the use of GM Wavetables is useful for live performances where the performer makes use of midi files and/or styles (one man band). There is a need to quickly respond to program change midi commands, e.g., when changing from fills to main variations, etc. Plus in this situation one may be willing to accept a small reduction in quality to achieve this objective.
Another use of GM Wavetables is for a quick run through of your musical ideas before you go for heavy duty recording or hiring a band or orchestra for you project. It provides an alternative to hardware based solutions. If you want to spend the money then you can usually do much better as compared with hardware alternatives (with the exception of course of a not so good control surface).
So when you say huge GM Wavetable that is a relative term. All other things being equal such wavetables will give you the best reproduction of the real thing. It is up to the muscian to ensure that the styles or midi files are of good quality. Here again one may make a difference or compromise between what one uses for live performances vs studio work. The thing is to do the best you can in all categories of music making.
[This message has been edited by Frank L. Rosenthal (edited 12-22-2005).]