Synestive :
You will almost certainly see some type of performance boost from the new card, The question is how much. This board:
http://pcpartpicker.com/part/asrock-motherboard-h97mitxac has pcie 3.0 and will cause less of a bottleneck but mini-itx is really not that good for gaming. If I were you I would seriously consider grabbing a full atx case and a better motherboard.
What moronic forum myth are you subscribing to to come up with that BS? There is absolutely no evidence or reasoning that you can possibly come up with to back such a stupid claim. Mini ITX is a physical form factor. Nothing more. It still uses the same chipsets, the same chokes, the same PCIe Lane designs. Is there a potential performance deference between a cheaply made board that happens to be using the H81 chipset versus a ROG series Z97 motherboard? Sure, but the particular form factor of the motherboard has absolutely NO bearing what-so-ever on that. So yes, TECHNICALLY you may see a miniscule difference in performance between a top of the line gaming motherboard and your current board during synthetic benchmarks, but in actual real world use, you will never notice it and it certainly isn't worth a $200+ investment and form factor/case change. Especially as I assume that your original H81 choice was a value based decision to begin with.
Don't listen to morons that exist only to spout off nonsense theories they read somewhere else posted by other morons and do your own REAL research.
I don't post very often because I prefer to take my questions and search out factual evidence to support, or disprove theory. Not just soak in opinion based nonsense shouted out and repeated as doctrine by idiot fanboys and, for all you know, 13yr old children that watched too many old hacker movies and think that qualifies them to have an opinion.