The C150 is not quite that slow, and the C152 is not quite that fast!!! It is quite reasonable to expect 100 mph out of a 150 (which is about 87 knots), and maybe 95-100 knots from a 152. FWIW I typically show about 105 indicated on the Sundowner. I can coax it up to about 120 true at higher altitudes though.
I had the 130hp model - FRA150L (Aerobat). Cruise at 110-115mph. Better climb also with the 130hp.
40% flap - I generally used 30% and used the 40% when it was needed. I have gone around with 40%. It is harderwork than at 30% just requires you do it properly as you were trained to do so.
Nice machine had lots of fun from mine.