FT: maneuver or better weapon arcs?

I played a battle the other night with ships that had thrust-6 and
1-arc class-3s.  The enemy got up to speed 18 and I had a hard time
keeping him in my weapon arcs.	Is this usual?	Are high speeds
common?

I'm considering to lower the thrust to 5 and adding 1 arc to each
of the two class-3s (FP+F, F+FS) but hate giving up that extra turn.
A good idea or stay with my original design?

Btw, these are from my Klingon designs:
"D6" - mass 54, 2 class-3s (F), 1 class-1, 3 armor;
"D7" - mass 84, 3 class-3s (F), 2 class-1s, 5 armor
(the central class-3 could be a pulse torpedo launcher);
both - average hull, thrust-6, FTL, screen level-1, 2 FC.

It works out that lowering the thrust to 5 lets the D6
expand each class-3 by one arc, and the D7 the same plus
an extra arc for the 3rd class-3.

Glen