Mike, make yourself a spreadsheet with the landing weight and all the
V-speeds.

use the formula:

V(?)landing weight = [squart root(Wlanding weight/Wgross weight)] * V?
gross weight

Where W is the weight and
? = best angle, x
best rate, y
glide
stall clean, s
stall dirty, so

Also keep in mind that V-speeds are different when the gear is up and
the gear is down.
Some manuals will give you both the gear up and gear down Vx and Vy
speeds, most do not.

The PA28R-201RT, for example,
From the POH, Section Four, Normal Procedures

Vy = 97 gear up, flaps up
= 79 gear down, flaps up

Vx = 79 gear up, flaps up
= 73 gear down, flaps up

Remember, these are gross weight speeds (approximately 3600 pounds for
the Saratoga, right?).