man once again you messed the things up.you write very dramatic staff and sail away from the story.in fact you know i dont ride 48size and talking about 58size frame,its just the next bigger size.but again i didnt insist on that at all.i just wanted a factual answer from someone who tried out,away from what the calculators and the stores say.but then again,i respect that in some extent.if something is big,then its big.period.i dont doubt that in any manner.

in any way,surely the company wants to save every bit of a penny can from even 1 mm of each frame.thats called profit.thats why they "invented" compact geometry with slopping tubes etc.its not you who benefits from that,its the company that puts out 3-4 sizes to cover the shortest to the tallest guy out there.and say to you "comon buy the small size be a "pro"(why to order you the exact size,it costs to us-profit) and put a 3 feet long stem and itll be ok (profit again).haha.

and fyi my current steel everyday beater (ex-mtb) counts 57 effective top tube(its a bit slopping though 15 years old.)and rides decent on quill and a llittle riser bar.
and of course,there are compatibillity windows just like in my example,the campy-shimano mix.if you search youll find some more.its not a shame to mix what youve got,disputing the "official" sacred marketing manuals,and find another path your self.its called creativity.(in fact when i searched the net for shimagnolo mix,only one said that 10sp shifter to 8sp work.the rest higly doubt and discourage any sort of mixing,and some others used adapters that some cases require).see for yourself.
have a nice day.