I would ideally like to reach a repeater about 70 - 80 miles away from
me.

How many miles away don't mean much.

I have no problem reaching a repeater 100 miles away with only
5 watts & a Open Stub J-Pole. BUT, this is a big BUT.
My location in Cheyenne WY is 1000 feet higher than Denver,
and the repeater is on a mountain top 3000 feet above Denver.
That is true line of sight if you could see that far.

Now if you live in the flat lands of NE with antennas only 30 to 50 feet
high. You would be lucky to get 40 miles with 50 watts.
If you live in a valley in the mountains you may only get 4 or 5 miles.

It all comes down to Location, Location, Location.

73 Al Lowe N0IMW

Arrow Antenna