As above, I've read up on this but couldn't find a clear answer and I'm an idiot when it comes to wheels.

2000 Magna TH Sport, not lowered. If they do fit, will I need to roll the guards?

Thanks in advance

I had 18x8 +45 on my TJ Advance without issues. I think yours should be fine (with an appropriate tyre such as 235/45R17)

Check out http://www.rimsntires.com/specspro.jsp ,and put 205/65 15x6 +46 as the first tyre and your prospective ones as the second (say, 235/45 17x8 +44) and you will see the differences in clearances to suspension, guards, etc...