Are the plastic type pressure tanks better than metal?What is the average life on tanks and are they all in the same ballpark?I have a welltroll wx-202 20 gal that is probably shot its about 8 yrs old.Sears has simer and tractor supply has dri something,grainger has dayton in the catalog,on **** they have a plastic one so does grainger its a dayton too.What would a 35 gal tank do for me compared to a 20?Is it all about pump cycles or does the pressure last longer with a bigger tank? thanks for any info steve.