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
['https://outdoors.stackexchange.com/questions/3909', 'https://outdoors.stackexchange.com', 'https://outdoors.stackexchange.com/users/2174/']
Yes, there is definitely a performance difference between different types of kayaks. In fact, there are performance differences among the same types of kayaks. For example, a 14-foot kayak will always track more straightly than a 10-foot kayak. A wide recreational kayak will always have more primary stability than a narrower touring kayak.

Even if you both get the same type of kayak I suspect you'll find they work differently for each of you. No doubt you both do not weigh the same -- if you're heavier, a given kayak will sit lower in the water than for her. That may result in increased stability, or it could mean that you capsize easily. Alternatively, consider height and armspan: if she's short she may find it difficult to paddle in a wide rec kayak where the paddle is constantly bumping the edge of the boat.

In short: you should each look for a kayak that suits you. That means you will see performance differences between the two kayaks, but if the boats really do suit each of you, that won't be a problem because you've found something that fits well. As to a fishing kayak specifically, if you get a longer kayak than her you'll likely be able to keep up with her on a day trip (though at the expense of maneuverability).

Of course, keeping up with a partner is about more than the just the kayak. The paddle will also make a difference (especially its weight as it relates to your fatigue), and paddling technique can be a big difference between feeling good at the end of an outing and feeling whipped.
I have been considering just the same. I have come up with two kayacks that I like. The first is a fishing kayak by kudo. It tracks well and speed is good. I have a strong upper body so it makes it easier for me but its all in the core. Try different techniques as you will get tired just doing one.

The other kayak is a 14 foot looksha by Necky. I have been eyeing that one for 3 years now. It is a sit in oh the kudo is a sit on top which I stood up in and tried paddle boarding on it. Great stability. The looksha tracks and maneuvers great.

Not stable enough for fishing, what are you going to do when you land the mother of all fishes? How you bring that into the boat? Consider what you do more spending time with the wife or fishing in a kayak?