I've had the SL1 for several months and I love it. So does my wife - as it's now with her in Ireland and Scotland for another week or so. Couple weeks ago, I evaluated the 100-400mm II (at the beach) & while that lens spent most of its time on a 1D3 with or without sticks (monopod mostly), I did remove the foot one afternoon and mounted it to the little SL1. Amazingly, I found it to be a VERY usable combo. Thought I'd hate it, but - in fact - I probably had my most productive daylight session with that combo. But YMMV. i was also evaluating the 11-24mm (that's a separate story. In one word: wow!).
I've also recently acquired the M3 w/EVF & today's 4 EF-M lenses from a poster at "FM". While I'm fumbling a bit with this newest addition to my kit (a 1D3, 5D2, 5D, 70D, 40D, SL1 & Fuji X100S collection), so far, I am liking what I've seen - a lot.
the new EF-M lenses have a more solid, compact, metal feel - impressive build quality. IQ is also impressive & they feel much nicer than the EF-S/EF STM lenses - all of which I think I have except the 24-105 stm (as I have the L variant of that lens).
these existing STM lenses (10-18, 18-55, 18-135, 24, 40, 50 & 55-250) seem to function well (fast and accurate AF) on the M3, I find myself using the 18-135mm - despite it's greater mass when added to the adapter - as much or at times more than the stm primes. I like its practical range and image IQ,
the other EF/EF-S lenses? I'm still experimenting - so my opinions are all over the place - depending on the lens in question. someday I'll master these combinations - what works well vs what does not - but I'm not depending (for use on the M3) on much of my non-STM collection of EF & EF-S glass - at this point.
I do know that my APS-C Tamron EF 16-300mm VC PZD - does not work AT ALL on the M3. It fails to AF a couple times before causing the camera to essentially shut down. I've heard this is also true of other similar Tamron lenses on the M3. tamron has acknowledged this problem - but, to date - has no fix.
In the 3 or so years since Fuji released its MILC system, they have released 16 high quality lenses. This is in stunning contrast to Canon's 4 EF-M STMs. Were I not so invested in the Canon ecosystem, my X100S would have a growing number of Fuji companions.
But, I'm hoping that Canon quits protecting its existing DSLR market positions - as it sure seems that Canon fears cannibalizing its current standing with professional and advanced amateur photographers. Arguably not unlike how kodak protected their film customers from that evil onslaught of binary code.
I'd suggest Canon review how kodak's old protective strategy played out.
Anyhow, while I love the SL1, don't be too quick to dismiss this M3. While I do not think this MILC has reached its design potential, I think it is now a high quality camera - worthy of SERIOUS consideration. I hope canon's recent decision to belatedly announce an October USA/CA launch is finally an indication that they will aggressively develop their mirrorless (M) system.
Then again, this is the third time in three years that this precise rumor has circulated.
But this time I've bought into the M system. In simple terms, I want to use this camera. I really look forward to seeing more reviews and user reports. Also, maybe someday somebody will publish a real guide. HINT (hoping DB finds this) - as of today, the only english resource I find is canon's PDF (I'm not a fan of digital manuals - aka binary sleeping pills).
Anyhow, the SL1 is a fun little camera. I really like it, but I keep bumping into the numerous compromises Canon designed into it - so as to not have it compete with its more expensive rebel siblings.
I'm interested to see the specs on the rumored SL2 (august slipped by without a peep).
Have fun and enjoy!