Haha! dude I feel like we had this discussion.
It's important to add a few key parts when picking your numbers. I call it the "law of 3's" - meaning you MUST pick a multiple of 3 as the final number.
1st pick a speed range of 10's. this should be 1 more than your actual speeds. for example if you're realistically going 35 you pick 40's.
Then the law of 3's comes in, if you want to be going "in the 40's" you pick a nice steady "43". The 3 is, as you mention, oddly specific enough to be believable but not requiring you to claim as high as 45. Therefore being caught at only 35 you can still fall back on a "bad day" or faulty weather.
If you're looking to break the 5 and tip-toe closer to the next multiple of 10, 46 is a convenient easy "over 45"
and if you wanna go all out, you gotta claim the 9. 49 is "basically 50" and "just a little bit of regearing and it'd be 50, but I'm OK with 49" exudes a certain modesty and suggests honesty, letting you evade prying questions or having to back up the claims