Been mining for approx. 3 days now and I'd like to know if my numbers are "normal"

Hey guys! Been reading you for a while now, but subscribed only yesterday.

I just built a new home PC that I use for mining. I will sometimes work on it, but I'm no gamer, so the discrete GPUs are only used for mining. And right now, I don't use the PC for anything but mining, just to make sure I don't interfere with it.

PC specs:

• Sapphire Nitro Radeon R9 390 Backplate (8 GB) x2 ... bought used from a gamer friend who couldn't stand the heat anymore! :-D
• Intel Core i5 6400 (has integrated GPU, so I can work with the PC when it's mining)
• G.SKILL Ripjaws V Series 16GB DDR4 2133 (PC4 17000) (2 x 8GB)
• EVGA 1000GQ 210-GQ-1000-V1 80+ GOLD 1000W
• GIGABYTE G1 Gaming GA-H170-Gaming 3 (rev. 1.0)

Software:

• Windows 10, fully updated
• Crimson drivers: 16.9.1 (also tried 15.12 as often suggested)
• Claymore's Dual Ethereum+Decred_Siacoin_Lbry AMD+NVIDIA GPU Miner v7.2 Beta

I've been mining on Ethermine since late Thursday night. At first, I was mining with only one GPU as was still waiting for my new case, and the old one was too small. If I'm correct, I had an average of 30 to 40 shares per hour. Since I added a second GPU, it varies a lot between 45 and 60 shares per hour. Effective hashrate is probably where it should be for the GPUs I own: between 55 and 60 MH/s. 60 seems pretty standard for two R9 390.

My questions:

- Is 45 to 60 shares per hour "normal" for my hardware? (uncle rate between 0% and 5%)
- Is such a fluctuation normal? (I guess it depends a bit on luck/probabilities)

Thanks a lot for your time and help!

By the way, I'm new to mining, but I am an experienced software developer as well as a part-time sysadmin (Linux and Windows). You can go technical on me.