Lv 50 Archer then Bard????

[Tayders]

I did a test at level 30 and with same gear, I got a 10 dexterity/attack power buff on Bard.

Can anyone confirm?

[Bardo]

Can anyone confirm?

Yes, you do get a dex bonus when you equip Bard.

But more important than that, you get Bard AF at 45. That gear dominates anything you can get with Archer, so you will be gimping yourself a bit for your last 5 levels if you continue leveling without unlocking the job.
If you're soloing, then you can probably level to 45 and you won't notice much difference.
But if you're doing dungeons, you need to aim to have Bard unlocked by around 40 because Mage's Ballad and Army's Paeon can actually make a difference by then, even in 4 mans.

It really doesn't take that long to get pugilist up to 15 and you get a couple of FANTASTIC skills to help you level your archer/bard in Second Wind, Haymaker, and Internal Release.
Just be sure to put on your mog hat, eat food for the exp bonus, and go steamroll a starting zone.