I hope to start brewing this summer, so I am collecting my supplies and hardware needs. Right now I'm thinking about my brew kettle size. Because I would like to brew using a partial mash process, and producing 5 gallon batches should I get a 7.5-8 gallon kettle or just get a 10 gallon instead?

A 7.5-8 gallon kettle will work fine.

However, if the 10 gallon kettle isn't inordinately more expensive (and it will fit on your burner) I'd go with the that one. This is simply because the added space will make boiling overs a bit less likely.

When I brew extract and specialty grain batches I use a smaller (~8 gallon) kettle. I mean, the 15 gallon converted keg is a bit over kill when you are making just a five gallon batch. At any rate. I wish that kettle was a bit larger simply because I really have to watch it to avoid boil overs. One still may have that problem with a 10 gallon kettle but I believe you'd more likely to catch it in time without having hot wort spewing onto the floor.

Note that I am assuming the 10 gallon kettle is taller that the smaller volume kettle and not simply larger in diameter. If it is not significantly taller then my boil over arguments kind of fall apart.

Having a larger kettle would still give you more options which is always nice, however.

It basically comes down to economics. A 7.5-8 gallon kettle will work fine and serve you well for years. However, if you can afford it, the 10 gallon kettle would be really nice to have. Even if you move up to all grain brewing and get a larger kettle whichever one you get now will still be useful. I also use my smaller kettle for decoction mashing 10 gallon batches.

I hope this helps rather than muddies the issue.

- Scott