Need help from the rest of the SBC gurues..

I have a 82 elky w/ a slightly modified 302

Recently changed carbs ( no probs) and was out on the shake down drive...
took engine to about 5500 rpms..ran out ok...but when i arrived back to the shop I noticed watrer underneath....took a look and found that one of the waterpump to block gaskets had started leaking...

So here is the question...how much pressure i is there in the cooling system at 4500-5500 rpm??

standard cooling system ..stock thermostat..no modifications to cooling system
new 3 core radiator installed 2yrs ago at overhaul...never a problem with cooling system prior to this..