I had a 1986 Mustang with a 2.3 liter 4 cylinder engine that I hopped up. It had big valves, port work, Esslinger circle track intake, 500 cfm Holley, JR header, etc. I swapped out the original 73 jets for 69's. then 65's. The 69's were much better for power and didn't run rich like the 73's. The 65's were still great for power, but a little down on power at the top end, with no rich issues at all and 3 to 4 mpg better gas mileage than the 69's. Ran it with the 65's in the UK for 3 1/2 years, then 69's in Germany for 3 years. If I wanted a decent combo of mileage and power, I'd go for jets around the 65's. If you want a little more top end, I'd say the 68's you have would be about perfect, but might be a little rich down low. IIRC, I used a 6.5 power valve after checking vacuum reading at idle. Tried an 8 and a 6.5, but settled on the 6.5 PV. I used a 31 shooter instead of a stock 25 for a little more fuel shot for transition from idle to power circuit. That may be dependent on your little plastic throttle cam though. IIRC you measure for vacuum at idle and then cut that reading in half to be close to what PV you need.
Darrell