The i7 will out perform the xeon. Since it's a dead even comparison, both have the same amount of cache, ht etc, the 1231v3 is 3.4ghz and will turbo to 3.8ghz (3.6ghz if all 4 cores are loaded). The 4790k starts at 4ghz and will turbo to 4.4ghz (4.2ghz if all 4 cores are loaded) without even overclocking it. Almost 18% (17.6%) faster than the xeon.
When overclocked, the 4790k can often reach 4.6-4.7ghz (some reach higher). Even taking 4.6ghz as a 'mild' overclock, that makes it 28% faster than the xeon. Factor in the igpu the xeon lacks (igpu enabled xeons cost considerably more than the 1231v3) and the price of the 4790k is pretty much in line.