In the U.K. postcard paper which is slightly less than 6x4 but is portfolio paper is now about $70 per 100 sheet box, add the percentage increase in price that warmtone RC seems command over normal MGIV then compute what this would be in 5x7 or heaven forbid 8x10 and that may be the answer as to why Ilford doesn't make a warmtone version of Portfolio RC.
No-one would buy it
In the U.S. of course the Ilford pricing policy might mean that these prices would be nothing like as high
pentaxuser