The Azensis rt615's are dirt cheap. For your size- $111 a piece at vulcan tire sales. Worth trying out. If they start to lose some grip as the day goes on, you could always join Kenny and Paul and have your water sprayer handy on the grid.
Muddy- you have a light car and you are smooth and easy on your tires. That's not saying you aren't pushing it hard enough, just not over-stressing them.
I think they will last you longer than you think.
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Drew Scoda
'87 Mustang