900 pixels enlarged to 10 inch at 360 PPI is 4x enlarged or effectively 90 PPI, 5616 pixels enlarged to 3 metres at 360 PPI is 7.57x enlarged or effectively 47-48 PPI. I don't see how the former could be worse than the latter, and the latter can look darned 'good'.
I just did a test...going from 900 x 900 to 10" at 360 prints out like crap, lots of ringing and artifacts from the upsample (bicub smoother in PS)....taking an image that is 5616 to 3 meters will also look like crap unless the viewing distance is from a lot further away than a 10" print. Yes, you can massage it and make a larger native file size look better, but it'll never look as good with a close viewing distance as a higher rez original. And no, I didn't print the 3 meter image out...just looked at it at a 50% screen zoom. I suppose if you did a lot of work on the file and added grain, you could look at the printed piece and find it acceptable from a distance.
I once did a job for Motorola that was printed 48' x 96' and it looked pretty good coming off a 60MB file. Course it was for a billboard at the Atlanta Olympics and the intended viewing distance was the other side of the stadium...
But trying to get a good print at 10" from 900 x 900 starting pixels? No, not unless your acceptance is a lot lower than mine...maybe I'll adopt yours.
Jeeesh that would mean I wasted a ton of money buying an 80MP MFDB and stitch images together to get high rez prints. What a waste on my part, huh?