Are there even that many single threaded applications left that require the performance of an i5 nowadays?
Saras, don’t forget that *everything else* that isn’t multi-threaded is generally single-threaded (or performs like a single-threaded application). And that includes the large majority of software OP is likely to use. OS startup/wakeup/resume, installer archive decompression, file-scanning, etc are still largely single-threaded, and the i5 is the clear winner in that category
Besides, the
FX-8350 demonstrates no significant advantage over the IVB i5 in lightly multithreaded applications either, where bottlenecks may lie elsewhere (e.g. memory/cache bandwidth). That means that even for multithreaded applications (Photoshop, archive compression/decompression, etc) the i5 stands toe-to-toe with the 8350 in quite a number of them.
The 8350 sees a significant advantage over the i5 only in
heavily multithreaded workloads, e.g. rendering and encoding. If this is not going to constitute the large part of OP’s usage scenario (keep in mind that video-editing/CAD doesn’t mean you’re rendering final product all the time), he will be better off with the i5.
A quick look at Newegg tells me that
all the 9-series AM3+ motherboards they stock are ATX. OP did mention he will probably stick to a mid ATX tower (I’m assuming this means ATX mid-tower) which doesn’t exclude ATX motherboards, but since he mentioned ITX builds I presume he doesn’t want to just throw out micro-ATX options either. Just another thing to keep in mind, in case he tries to shoehorn an FX-8350 into an AM3 motherboard *cough*

And if we go with the set budget question, mainstream gaming level ITX boards don't really exist, you basically have the choice of going either office or extreme
Not true. They exist at <=$100 already (H67/H77), and despite lacking OC options are quite "mainstream gaming"-capable.