Newbie here.... any drawbacks from a frame that's a bit too big? I just picked up a bike with a standover height maybe .5 to 1 inches too tall (its a 56 when a 53 would have been the perfect size)........ Top Tube length seems find, but I need to adjust the height.

Standover height it not the correct way to size a bike anyway. If everything else seems fine, ride it and enjoy.

I just discovered this as well while shopping the last month. If I went strictly by stand over height, I was looking at 63-64cm. frames. But once I was on them, they were way too stretched out for my upper body to be comfortable. I ended up being fitted in a 60 cm frame with a stock stem, and only the seat slid back less than 1 inch. It feels comfortable, and I am glad ended up being fitted rather than going by strictly a stand over height.

I fit a 58 cm frame
But the length of the bikes are too long and ever extend my back.

I ride a 56 cm with the seat raised two inches and the head four inches.

Me straddling, top bar in crotch is cutting into me, but I can stand firm on the ground

now 53 is SHORT. You'd have to be 5'6''. I'm 6' and I fit a 56 well.

A larger bike could be nice if most of your height is in your back and you can still adjust your seat up and down for your pedaling.

I'm 6'3" and ride a 54. This info is useless to you as i have not given my flexability, proportions or the make of bike

When you say standover is 1" too high what are you measuring.
Traditional road frames with a horizontal top tube should have about 1" of standover clearance. Modern frames with slanted top tubes are designed to have much more, perhaps 3-6" of clearance.
If you are measuring up a modern frame using traditional methods the result will be too big, ie too long.

Generally, top tube length is more critical than standover. If you feel OK on the bike then its fine.

I'm 5'10" and I ride a 54 with not much seatpost showing. 110 stem fwiw. If I could get enough saddle setback, I'd ride a 52 with a 120 stem so I could finally get my handlebars lower. Much of my height is in my neck, though.