just my idea.

the C series is more like portable with go 7400 gpu, 13.3". smaller than FE series. so you will not have problem bring this notebook anywhere. (2.3 kg)
the FE series come with better gpu than C series which is go 7600, 15.4" screen, plus with camera built in. if you dont mind with the weight and the size, go for this version. (2.8kg)

when the notebook come with dedicated gpu, obviously the battery performance is lesser than the one with low voltage processor and integrated gpu.

performance wise: FE better than C, in term of processor and gpu.

but in your case, you want portability, casual gaming, video effects, 3d stuff, nvidia go7400 should be enough for you. upgrade with 2gb ram, you are set.

i suggest you upgrade ram not via sony, cheaper and alot of choice. but if they still give promotion for free ram upgrde , go for it (if it still available, before they have).

turbo cache is like sharing with system memory if only if they need to get more memory for graphic application. basically, those nvidia go series come with this technology. they have their own dedicated memory too for graphic application.

most gpu for mobile nowadays have their own dedicated memory + with extended memory (turbo cache as for nvidia) which is sharing with system memory.

as for go7400, have 32mb or 64mb dedicated + sharing with system memory up to 319mb  memory for graphic application. for go7600, 64mb or 128mb dedicated + up to 383mb share with sys. memory.

dont worry much about performance, they still decent than the integrated gpu.
just get better amount of ram according to your needs, you will be ok.

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Added on July 7, 2007, 11:38 pmi can say that obviously the one with dedicated memory give better performance, but the drawback is the amount of dedicated memory is limited for mobile. so they come out with sharing with sys memory to overcome the problem.

Why not go for FZ series? The ram you can upgrade ur ownself cost RM 140-150. If via Sony = RM 400. I asked before.