Hi Roel/Christina
Here are my 2c
My first DSLR was a E520 and I still think the overall photo at lower ISO esp colours are very good out of this camera and has a special texture/feel to it. Low light/High iso is quite disappointing from my view but its a known story and DR too.
I got a EP1 as my bday gift this year ( one year on after the 520 ) and I have to say I am blown away by its IQ especially in low light. I think DR is also better than the 520.
However the colours and texture are slightly different ( I think this is true of the 620 and E-30 also ) with the new 12mp sensor and True pic IV/V imaging engine. The high iso files respond well to pushing as well in Oly viewer or LR...
However, when it comes to focussing, I use the Pen with the m14-42 which is an ok focusser - about half the speed of my 4/3 14-42 on the 520 and the 40-150 (adapted via MMF1) isnt bad but not super quick. I have heard good things about the m.9-18 and the 17mm pancake but do not have them.
Low light focussing revelations from a recent experience shooting an indoor event. The 520 with 40-150 & 14-42 was hopeless in an indoors mixed light situation ( kids bday ). While the Pen wasn't fast the CDAF atleast focussed but both were beaten by compact cameras with an AF-assist ( not joking - very serious here - I think manafacturers are making a big mistake by omitting this simple feature and expecting one to get an external flash esp on the Pen )
regarding 620 vs the Pen - I think these are the differences
620 -
- OVF
- AF adjustment ( I suspect some feel this is invaluable )
- articulated screen
PEN
- No VF for Ep1
- Pricey but good EVF for E-p2 & E-pl1
- TruePic V is definitely a better imaging engine
- all Pens have a lighter anti aliasing filter than the 620 ( iirc) - the e-pl1 has a very very light one
- Shadow noise better controlled than 620/E-30
- Very Lightweight option with the m.z lenses
- Balance with HG/SHG I think would be hopeless
- Balance with regular 4/3 40-150 suprisingly good
For my use - I am wondering as an enthusiast, if I should just add a flash for my pen and sell the 520 - but can't make up my mind... esp given that I dont have any HG/SHG lenses.
Good luck with your search and purchase
[EDIT]
A couple of pics from my pen from a recent walk around for your reference if it helps. You can find more in my gallery
[EDIT]
Tx
Vidya