I've answered nearly 28,000 questions on the site but I don't think that I've ever been as much 'in two minds' about my answer as here!
A 4" pie will look quite tempting in a shop window
http://farm3.static.f...909588_9ec943e4db.jpg
but perhaps less so on a plate:
http://www.bighospita...t-usage_dnm_large.jpg
(I've obviously not measured those pies but they look about the right size to me!)
Someone (with a healthy appetite) going for a pub meal, for example, might be rather disappointed by such a small pie. This picture is probably more representative of the size of dish which they'd be hoping for:
http://www.essentiall...mages/cottage_pie.jpg
I'd estimate that dish as being about 6 or 7 inches long, by 4" wide, with a depth of around 2½ or 3 inches.
Actually, having typed that bit about the depth, I've made my mind up ('cos the dishes in your link are only 1" deep); they're not big enough!
Chris