You're going to lose money selling a Pentium to upgrade to a Broadwell, and you'll have a slower processor in the interim than just buying a decent Haswell now.
Waiting for something that's 10% faster is pointless. 10% isn't fast enough to be worth the trouble. If it makes you feel any better we have a whole bunch of (like 250+) homebrew workstations here ranging from i7-2600 to i7-4790, and the difference between them is probably 15-20% or something. They do software renders and 3D modelling all day and NOBODY can tell the difference between them. You'd need to use a stopwatch to realise that one encode/render takes 17 seconds on one and 20 seconds on another. If you're gaming the processor is even less relevant since your GPU is always the limiting factor unless you're using a single-core Celeron or something.
One other thing, Sandy > Ivy > Haswell may have given 5-10% improvements per generation, on average but that's an average based on many things. 0-3% improvements for gaming and 5-20% improvements for various encode/hw-accelerated CPU tasks. Games basically run no faster on Haswell than they do on Sandy, and I seriously doubt Intel will make great strides with Broadwell since they're focussing on mobile power reduction above all else.
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