time trial measurements for 55cm bike

Quoted message said:

I have a Giant ocr1 55.5cm mens bike.
I here that the frame is a day riders frame, not for racing and not
much aerodynamics, and geomeraty is setup for old grandmas. I my
pursuit to go faster i would like a better frame, a time trial frame.
The frame i want to get assuming it is geomeraraly sound is either
avaliabe in 54 cm or 57cm. That is my first problem. I am just over
6 foot.
57cm bike has a front fork wheel angle of 74 deg, and seatpost to back
wheel angle of 72.5 deg.
Is that good? and is that the main thing i should be looking at?
bottom bracket is 68 lower than the wheel axels.
top bar is 600.

or should i be trying to squeeze onto a 54cm? Originally the bike
shop said i need a 55cm bike.
If i went the smaller one, it would be lighter. but the bigger one
would be 30cm longer on the top bar, meaning i would be leaning down
more to get to the handle bars.

any help would be apprecieated.

55 cm for a six-footer sounds way too small. I'm 5'7" and ride a 54
or 55 cm frame--and no, I don't think these frames are too big for me
since I usually have the saddle almost as high as it will go and
prefer a 10 cm stem or longer.

Road bikes should really be sized for reach, not standover. This
produces the somewhat paradoxical result that riders with short legs
should ride larger frames than those with long legs, given equal
heights. I think Sheldon Brown's site gives some recommendations
along these lines.

For TT, it's common to use a smaller frame than normal. That way the
handlebars can be set lower and if you use a similar position as the
professional cyclists (as opposed to triathletes who seem to prefer a
more stretched out position) with the upper arms vertical, then you
don't need as much reach, either.