Changing drivers can in fact induce stutters or cure them, and that has been the history of FSX. Every now and then a driver comes out and FSX stutters with it, but then eventually it gets fixed in a later revision. As to nhancer, that alone won't do anything for stutters, at least not from my experience, and I don't see how it could because all it does it flips the same switches in the video driver that the Nvidia control panel does, with the exception being supersampling, since those switches are only available through the nHancer control panel.
If you really want to get the scoop on tweaking FSX see my thread over at Orbx.
The thread developed a great deal as I refined the tweaks introduced in the first post, so I recommend reading the whole thread, or perhaps find my posts near the end where I had refined the settings. The main tweak however, which I named "The Miracle Tweak", is to set a BufferPool value of 200MB+. The more video RAM you have the higher you can go. I run mine at 300MB, but guys with 1GB cards can usually run 400MB. This one tweak will eliminate stutters on most any Core 2 or i7 system. As with all tweaks a number of factors are involved and they must be balanced, so things like texture bandwidth multiplier can effect it if that setting is too high, for example. Read the thread and play around, as that thread has the keys to get any fast system running stutter free.