SELECT xyz INTO #Temp from SSMS is 5x longer in one environment than another First time posting, I hope I'm doing it right.

I'm a "dba by accident" who is learning a lot but admittedly still has a lot more to learn. Here is my brain dump:


Prod server has 5 million rows. I copied those rows to a Test server.
Using SNAPSHOT or READ UNCOMMITTED produce different elapsed times, but the ratio between Prod and Test is always ~5:1 (14 minutes:3 minutes with SNAPSHOT, 4 minutes:sub-1 with READ UNCOMMITTED)
Using STATISTICS IO ON reveals that most of the reads on Prod are logical (~90%) while none of the reads on Test are logical. I think that should mean Prod would be faster if anything.
Most of the time appears to be going to waits of type "PAGEIOLATCH_SH."
I don't think different statistics can matter, since no index should be used on an unfiltered, unjoined, unsorted query.
SELECTing the top n rows on both servers reveals a very linear scale... the ratio is always ~5:1.
The comparison is not apples-to-apples, but I think the only relevant differences are activity and storage.
I have performed the comparison when activity was next to nothing, and saw the same results.
I discovered that autogrowth was set to 1MB (ugh), which I have since changed but I wonder if this has led to fragmented storage at the file system level.
The database is on a separate volume from the Windows installation, but it does share a volume with tempdb and with a FILESTREAM store, which I assume could also lead to fragmented storage.
The "optimize drives" windows utility says the volume is "OK (98% space efficiency)" which seems to suggest that maybe file system fragmentation isn't a problem.


Questions:

Are my thoughts and assumptions above correct?
Is there anything I'm blatantly overlooking in my thought process?
What are good candidates for the next steps in this troubleshooting process?
What other information can/should I have provided?

Thank you for your attention and help!

EDIT: Added rest of time information in 2nd statement.
For me it sounds like issue with tempdb.. What you could do- check how many files you have on each server- you can see recommendations here. 

Are they big enough and not growing when you doing inserts? What about log file of tempdb?
if they are growing- best would be to expand them before (and keep that way).

One more thing you can check- if they are growing, you can probably make it faster by using instant file initialization.