Last year my wife and I rented a couple of SOT kayaks and used them to paddle around our local lake. We enjoyed it so much we have decided to purchase our own this year.
We are looking at some entry level kayaks to use at the lakes and rivers here in Illinois. 
I am also an avid fisherman and I would like to get a fishing kayak but I don't know if there is a difference, performance wise, between a fishing kayak and a touring/recreational kayak. I don't want to struggle to keep up with my wife if we decide to kayak for 4 to 5 hours on a river or lake.
Would I be able to use a fishing kayak like a regular touring/recreation kayak?

Thanks
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I have used a touring kayak for fishing, and it works out ok. You can rig up a rod holder in your cockpit, but paddling is a bit awkward, though this is probably also a problem with any kayak used for fishing.

It might be somewhat difficult to use a fishing kayak on overnight trips given that most fishing kayaks are sit on top (SOT) and have no internal storage.
I would recommend checking out something like Hobie's Mirage pedal driven kayaks. With their spiffy pedal drive, you can trivially outrun(outpedal?) just about anyone while hardly breaking a sweat. Additionally, because you power yourself with your feet, your hands are free for fishing. The mirage drive is also quiet as a corpse. No splashing sounds from your paddles, whatsoever.

A guy I know has one of their fishing-specific models, and loves it.

However, if you ever want to go on an overnight camping adventure via your kayaks, the storage capacity of the Hobies is pretty bad, and while in general portaging kayaks is no fun, portaging a Hobie kayak would be especially miserable.

Otherwise, you could try getting a tandem traditional kayak. Perhaps you can sweet-talk your wife into paddling while you fish?