Yeah, it's hard to tell anyone for sure what to do, since everyone has different hardware budgets.
If things are tight, there's two more considerations which would be downgrade / sidegrade. Cheaper than the i5/i7 route, and also lower performing.
wait for the Haswell i3s to be out and go with one of those. video conversion speed would be slower than a 920, but really not as much as you might think for a dual core. All those little IPC improvements add up, plus HT, plus extra clock speed over a 920 means it actually performs on-par in some cases.
http://anandtech.com/bench/product/47?vs=677
The Haswell i3's will be marginally faster than that comparison. The IB i3 encoding benchmarks range from ~equal to ~60% with an average around 80-85% the speed of a stock 920. A downgrade, for sure, but would be a cheaper solution to lower power consumption and the more modern cores would be faster in anything using 1-2 cores.