Confused as to whether you mean Valor Cuisses (legs) and Heavy Allagan Flanchard (feet). You should be getting Valor Cuisses anyways b/c of the higher parry and acc over Allagan Legs (so you can switch in gear w/ lots of parry and little to no acc like Allagan Feet, Surcoat, Valor Gloves, etc.)

You should not be considering getting Valor feet over Allagan for any reason but vanity.

Aim for 475 acc without food and you'll be fine.

Edit: And if you're main tank you should be eating parry/vit food like La Noscean Toast and eventually Finger Sandwich.