Leopard should run better on your Macbook becuase it has been designed for intel chips aside to Tiger being ported to work on intel chips, so with the fact it will run faster I think a few 3D effects should be easy.
I don't know what you've read or what you think you know, but Tiger was not "ported" to x86. NeXTstep (The OS that Mac OS X was based on) ran on x86, and Darwin (the open source core of Mac OS X) has always ran on x86. It is now common knowledge that a project within Apple kept up to date builds of the Mac OS X for x86, called Marklar. Some programs were ported over, some accessories and apps, and the rosetta part for running PPC programs on x86 was certainly brand new, but rather extensive builds of the Mac OS X has been x86 native for quite some time.
The Tiger release was the first release to the public though, so I'm sure there have been areas discovered where the code can be made faster. There is a difference between built-for and optimized-for. Leopard will undoubtedly be more optimized than tiger, but that doesn't mean tiger was in any way "ported".
The GMA950 is more than capable of the Leopard effects. It's a bad card for gaming, and I guess that's gotten it a bad rep, but it's not THAT bad a card.