I just bought some factory alloys and tyres that are said to have come off a TJ Magna.
As I was putting them onto my TE I noticed that they are a different circumference overall.
The rims and tyres I was running were 205/65/15's
The new alloys and tyres are 215/60/16's

The new ones fit fine, but my question is how will this affect my speedo and torque etc?
Any mathematicians here who can work this out for me?

It's a pain I didn't check cos I still have two good 15 inch tyres. I just assumed that cos the mags are factory Magna alloys that they would be the same size.

Depending on model Magna and Verada have 15, 16 and 17 inch wheels.
You can use either link to see how it afects speedo.

http://www.wheelsmaster.com/rt_specs.jsp

http://www.miata.net/garage/tirecalc.html

your speedo will under read. so you will be going faster than your speedo says. by how much really depends on a lot of things, such as tread depth on new and old tyres, how the tyre manufacturer measured the tyres, etc, but theoretically the new tyres are about 2.6% bigger in diameter, so when the speedo says 100kmh you would be doing 102.6kmh. but then you have to take into account what error margin your speedo already had. it may be that you are reading 5% out before the tyre change, so if it was reading faster than what you were doing it might be spot on now, etc

Thanks guys. Yes the difference is about 2.7%.
So 100kph on the clock is actually 102.7 in reality.

Just a suggestion, if you know what car the wheels came off, use the same speedo drive gear as is in that car. Takes about two minutes to change them.